diff --git a/docs/SLACK-HELPER.md b/docs/SLACK-HELPER.md
new file mode 100644
index 000000000..84fb65f21
--- /dev/null
+++ b/docs/SLACK-HELPER.md
@@ -0,0 +1,57 @@
+# Slack helper namespace
+
+`f.slack` is the first provider helper on the authored TypeScript surface.
+Calls return a `Step` immediately and must be awaited like `f.run` and `f.llm`.
+
+```ts
+import { flow } from '@relayflows/surface';
+
+export default flow('notify', async f => {
+  const posted = await f.slack.post('#releases', 'Release shipped');
+  await f.slack.reply('#releases', posted.ts, 'Details follow');
+  await f.slack.react('#releases', posted.ts, 'rocket');
+  await f.slack.dm('U123', 'Release shipped');
+  f.done('success');
+});
+```
+
+Provide a relayfile mount with a `slack/` directory.
+`flows check notify.flow.ts` refuses visible Slack calls when neither a mount
+nor a bot token is available, with `REFUSED [helper_slack.credential_missing]`
+and exit status 2.
+Direct bot-token transport is deferred: a token without a mount is refused
+as `helper_slack.mount_required`, before running the body. A header can declare
+`tools: { slack: true }` for calls hidden behind another
+function. The body is not evaluated during check; dynamic calls also check
+credentials when they are awaited.
+
+`RELAYFLOWS_SLACK_MOCK=1` bypasses credentials and network. Each call captures
+its stamped body in `<data-dir>/mock-writeback/slack/<step-id>.json` and returns
+a synthetic receipt. Message timestamps are `mock-<step-id>` and message
+references are `mock-ref-<step-id>`.
+
+The runtime uses the published `@relayfile/relay-helpers` Slack client with an
+explicit transport. Relayfile receives the adapter's canonical write path.
+Direct-token idempotency needs Slack-server timestamp deduplication, which
+mount writeback already handles; direct-token transport is deferred.
+`flowRunWritebackIdempotency(runId, stepId)` always returns `runId:stepId`.
+The process-tick stamper cannot replace this token, including for reactions.
+
+The existing kernel agent lease carries the helper's external write. Its
+instruction and successful `step.completed.payload.output` carry
+`{ type: 'effect', provider: 'slack', verb, params }`; output also carries the
+receipt and flow idempotency token. `effect.record`/`effect.confirm` retain the
+kernel's own lease key. No kernel vocabulary or protocol change is required.
+Other providers can follow this transport and effect-worker pattern.
+
+Receipts are persisted under `<data-dir>/helper-receipts/` before confirmation.
+`flows resume <helper-run-id> --data-dir <data-dir>` reattaches the helper worker
+and recovers the receipt. Retain the whole data directory across restarts.
+The kernel retains a crashed attempt's `step.completed(crashed)` and records
+exactly one successful completion on recovery. A confirmed effect is not sent
+again. An unconfirmed effect is retried with its original provider token.
+
+The authored executor still creates separate runs per step; it does not yet
+have a durable journal for the whole TypeScript body. Resuming a helper run
+finishes that effect, not the remainder of the authored body. Postfix callback
+gates remain unsupported by this executor, as for its other current verbs.
diff --git a/packages/sdk/package-lock.json b/packages/sdk/package-lock.json
index 46d619c46..1a6e52500 100644
--- a/packages/sdk/package-lock.json
+++ b/packages/sdk/package-lock.json
@@ -9,6 +9,8 @@
       "version": "2.0.8",
       "license": "Apache-2.0",
       "dependencies": {
+        "@relayfile/adapter-core": "0.5.24",
+        "@relayfile/relay-helpers": "0.4.11",
         "@relayflows/surface": "2.0.8",
         "@types/js-yaml": "^4.0.9",
         "ajv": "^8.17.1",
@@ -416,6 +418,19 @@
         "node": ">=12"
       }
     },
+    "node_modules/@isaacs/fs-minipass": {
+      "version": "4.0.1",
+      "resolved": "https://registry.npmjs.org/@isaacs/fs-minipass/-/fs-minipass-4.0.1.tgz",
+      "integrity": "sha512-wgm9Ehl2jpeqP3zw/7mo3kRHFp5MEDhqAdwy1fTGkHAwnkGOVsgpvQhL8B5n1qlb01jV3n/bI0ZfZp5lWA1k4w==",
+      "license": "ISC",
+      "peer": true,
+      "dependencies": {
+        "minipass": "^7.0.4"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      }
+    },
     "node_modules/@jridgewell/sourcemap-codec": {
       "version": "1.5.5",
       "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz",
@@ -440,6 +455,155 @@
         "node": "^22.20 || ^24.12 || >=25"
       }
     },
+    "node_modules/@relayfile/adapter-core": {
+      "version": "0.5.24",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-core/-/adapter-core-0.5.24.tgz",
+      "integrity": "sha512-bOQRuBoAw2RlYs30RtKsOvXlXzcRx4owhHdj384hPrznBIY3U4ZYcb4pVfzreW9TStHEiX7EguUyqhD9g8DJmA==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@scalar/postman-to-openapi": "^0.6.0",
+        "cheerio": "^1.2.0",
+        "minimatch": "^10.0.3",
+        "yaml": "^2.8.1"
+      },
+      "bin": {
+        "adapter-core": "dist/src/cli.js"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/adapter-linear": {
+      "version": "0.4.12",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-linear/-/adapter-linear-0.4.12.tgz",
+      "integrity": "sha512-obICrTmIkVKXX0vAjGiezOK/cu3iUH6i67fuKLe7Fqcp/Upwrsr70Ap68YxyMvpNOvE4TdbbM1vU+2uGXwM5sg==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@relayfile/adapter-core": "^0.5.18"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/adapter-reddit": {
+      "version": "0.2.9",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-reddit/-/adapter-reddit-0.2.9.tgz",
+      "integrity": "sha512-/ZWkr4SguRRCk4fY6DEtP5NVUHSMWP66GtMou4NJOcf5PaxYSa0ceSVxAN/IcTBG6JqdtbqB4IoWn8V9d/JC3g==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@relayfile/adapter-core": "^0.5.15"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/core": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/core/-/core-0.10.57.tgz",
+      "integrity": "sha512-oKwNJKGovzdl/6IF3sSVZFsiG2ITH7jXnmFgxbCIYPZ+J7QsQ2zvBhT35sPGiNcD4FfiMpyX9OB8LJXOefNdcQ==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/@relayfile/mount-darwin-arm64": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/mount-darwin-arm64/-/mount-darwin-arm64-0.10.57.tgz",
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+      "cpu": [
+        "arm64"
+      ],
+      "license": "Apache-2.0",
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "peer": true
+    },
+    "node_modules/@relayfile/mount-darwin-x64": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/mount-darwin-x64/-/mount-darwin-x64-0.10.57.tgz",
+      "integrity": "sha512-5Ze1a16Mxc2PTj2Q+AdtRZIMKQ4sxJIIXwPjdWD+9rTMEQeqs7xzSZ1WRIjI89FzyNHBjx/+gzD9FK8Kjuc7Yg==",
+      "cpu": [
+        "x64"
+      ],
+      "license": "Apache-2.0",
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "peer": true
+    },
+    "node_modules/@relayfile/mount-linux-arm64": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/mount-linux-arm64/-/mount-linux-arm64-0.10.57.tgz",
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+      "cpu": [
+        "arm64"
+      ],
+      "license": "Apache-2.0",
+      "optional": true,
+      "os": [
+        "linux"
+      ],
+      "peer": true
+    },
+    "node_modules/@relayfile/mount-linux-x64": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/mount-linux-x64/-/mount-linux-x64-0.10.57.tgz",
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+      "cpu": [
+        "x64"
+      ],
+      "license": "Apache-2.0",
+      "optional": true,
+      "os": [
+        "linux"
+      ],
+      "peer": true
+    },
+    "node_modules/@relayfile/relay-helpers": {
+      "version": "0.4.11",
+      "resolved": "https://registry.npmjs.org/@relayfile/relay-helpers/-/relay-helpers-0.4.11.tgz",
+      "integrity": "sha512-J9S2L+dVRQcxv32BxMq+xEqpBJoG1mNzo1E/CCXY4LYUSl0euZD0ZayaFMcpBhGqx+2IDNiSlGjFun/YQk9OqA==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@relayfile/adapter-core": "^0.5.15",
+        "@relayfile/adapter-linear": "^0.4.11",
+        "@relayfile/adapter-reddit": "^0.2.9"
+      }
+    },
+    "node_modules/@relayfile/sdk": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/sdk/-/sdk-0.10.57.tgz",
+      "integrity": "sha512-9AJIEyyruqVogbdqVfY7q0pjuXJy8IhzxR/1pvwWJiybU1BZO8LFNurlFePTAo/uhLG9cshr0YJRBxv2WbG0Sg==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "dependencies": {
+        "@relayfile/core": "0.10.57",
+        "ignore": "^7.0.5",
+        "tar": "^7.5.10"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "optionalDependencies": {
+        "@relayfile/mount-darwin-arm64": "0.10.57",
+        "@relayfile/mount-darwin-x64": "0.10.57",
+        "@relayfile/mount-linux-arm64": "0.10.57",
+        "@relayfile/mount-linux-x64": "0.10.57"
+      }
+    },
     "node_modules/@relayflows/surface": {
       "version": "2.0.8",
       "resolved": "https://registry.npmjs.org/@relayflows/surface/-/surface-2.0.8.tgz",
@@ -799,6 +963,37 @@
         "win32"
       ]
     },
+    "node_modules/@scalar/helpers": {
+      "version": "0.5.1",
+      "resolved": "https://registry.npmjs.org/@scalar/helpers/-/helpers-0.5.1.tgz",
+      "integrity": "sha512-9VvPfv8b+YZVIFwR3SWeq4Y8ij/kU3/kf2M6NKcbf2iVyh63d8s0ssap5m/nOhiz/Puidv/29MAJlJCA0LRssA==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=22"
+      }
+    },
+    "node_modules/@scalar/openapi-types": {
+      "version": "0.7.0",
+      "resolved": "https://registry.npmjs.org/@scalar/openapi-types/-/openapi-types-0.7.0.tgz",
+      "integrity": "sha512-kN0PwlJW0de4bwQ4ib+mBHzKJUvBCyR/gwU4zLEq6SCbj+GfgYUh+2a0/yl1WYVUiSkkwFsHjfmQ8KjhR3HK0Q==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=22"
+      }
+    },
+    "node_modules/@scalar/postman-to-openapi": {
+      "version": "0.6.3",
+      "resolved": "https://registry.npmjs.org/@scalar/postman-to-openapi/-/postman-to-openapi-0.6.3.tgz",
+      "integrity": "sha512-Y/tMuRZG34wEfpTxDfXFp5o2X3ibb5ojGWupGJ9ZxkThCx7rOGydnszJPzEbgDK3eF6nJ6UuE7bCTpIEutYnPw==",
+      "license": "MIT",
+      "dependencies": {
+        "@scalar/helpers": "0.5.1",
+        "@scalar/openapi-types": "0.7.0"
+      },
+      "engines": {
+        "node": ">=22"
+      }
+    },
     "node_modules/@types/estree": {
       "version": "1.0.9",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.9.tgz",
@@ -981,6 +1176,33 @@
         "node": ">=12"
       }
     },
+    "node_modules/balanced-match": {
+      "version": "4.0.4",
+      "resolved": "https://registry.npmjs.org/balanced-match/-/balanced-match-4.0.4.tgz",
+      "integrity": "sha512-BLrgEcRTwX2o6gGxGOCNyMvGSp35YofuYzw9h1IMTRmKqttAZZVU67bdb9Pr2vUHA8+j3i2tJfjO6C6+4myGTA==",
+      "license": "MIT",
+      "engines": {
+        "node": "18 || 20 || >=22"
+      }
+    },
+    "node_modules/boolbase": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/boolbase/-/boolbase-1.0.0.tgz",
+      "integrity": "sha512-JZOSA7Mo9sNGB8+UjSgzdLtokWAky1zbztM3WRLCbZ70/3cTANmQmOdR7y2g+J0e2WXywy1yS468tY+IruqEww==",
+      "license": "ISC"
+    },
+    "node_modules/brace-expansion": {
+      "version": "5.0.9",
+      "resolved": "https://registry.npmjs.org/brace-expansion/-/brace-expansion-5.0.9.tgz",
+      "integrity": "sha512-ScQ4IuvIEF1TMlP7Zt+vjJ//9zlPb2SDcxWxM3bk8s6t6GGdJ7KO1dCcTidOPJKePW30LE/2cT7wCyPho9/Wxg==",
+      "license": "MIT",
+      "dependencies": {
+        "balanced-match": "^4.0.2"
+      },
+      "engines": {
+        "node": "20 || >=22"
+      }
+    },
     "node_modules/cac": {
       "version": "6.7.14",
       "resolved": "https://registry.npmjs.org/cac/-/cac-6.7.14.tgz",
@@ -1018,6 +1240,86 @@
         "node": ">= 16"
       }
     },
+    "node_modules/cheerio": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/cheerio/-/cheerio-1.2.0.tgz",
+      "integrity": "sha512-WDrybc/gKFpTYQutKIK6UvfcuxijIZfMfXaYm8NMsPQxSYvf+13fXUJ4rztGGbJcBQ/GF55gvrZ0Bc0bj/mqvg==",
+      "license": "MIT",
+      "dependencies": {
+        "cheerio-select": "^2.1.0",
+        "dom-serializer": "^2.0.0",
+        "domhandler": "^5.0.3",
+        "domutils": "^3.2.2",
+        "encoding-sniffer": "^0.2.1",
+        "htmlparser2": "^10.1.0",
+        "parse5": "^7.3.0",
+        "parse5-htmlparser2-tree-adapter": "^7.1.0",
+        "parse5-parser-stream": "^7.1.2",
+        "undici": "^7.19.0",
+        "whatwg-mimetype": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=20.18.1"
+      },
+      "funding": {
+        "url": "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/cheeriojs/cheerio?sponsor=1"
+      }
+    },
+    "node_modules/cheerio-select": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/cheerio-select/-/cheerio-select-2.1.0.tgz",
+      "integrity": "sha512-9v9kG0LvzrlcungtnJtpGNxY+fzECQKhK4EGJX2vByejiMX84MFNQw4UxPJl3bFbTMw+Dfs37XaIkCwTZfLh4g==",
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "boolbase": "^1.0.0",
+        "css-select": "^5.1.0",
+        "css-what": "^6.1.0",
+        "domelementtype": "^2.3.0",
+        "domhandler": "^5.0.3",
+        "domutils": "^3.0.1"
+      },
+      "funding": {
+        "url": "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/sponsors/fb55"
+      }
+    },
+    "node_modules/chownr": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/chownr/-/chownr-3.0.0.tgz",
+      "integrity": "sha512-+IxzY9BZOQd/XuYPRmrvEVjF/nqj5kgT4kEq7VofrDoM1MxoRjEWkrCC3EtLi59TVawxTAn+orJwFQcrqEN1+g==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/css-select": {
+      "version": "5.2.2",
+      "resolved": "https://registry.npmjs.org/css-select/-/css-select-5.2.2.tgz",
+      "integrity": "sha512-TizTzUddG/xYLA3NXodFM0fSbNizXjOKhqiQQwvhlspadZokn1KDy0NZFS0wuEubIYAV5/c1/lAr0TaaFXEXzw==",
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "boolbase": "^1.0.0",
+        "css-what": "^6.1.0",
+        "domhandler": "^5.0.2",
+        "domutils": "^3.0.1",
+        "nth-check": "^2.0.1"
+      },
+      "funding": {
+        "url": "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/sponsors/fb55"
+      }
+    },
+    "node_modules/css-what": {
+      "version": "6.2.2",
+      "resolved": "https://registry.npmjs.org/css-what/-/css-what-6.2.2.tgz",
+      "integrity": "sha512-u/O3vwbptzhMs3L1fQE82ZSLHQQfto5gyZzwteVIEyeaY5Fc7R4dapF/BvRoSYFeqfBk4m0V1Vafq5Pjv25wvA==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">= 6"
+      },
+      "funding": {
+        "url": "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/sponsors/fb55"
+      }
+    },
     "node_modules/debug": {
       "version": "4.4.3",
       "resolved": "https://registry.npmjs.org/debug/-/debug-4.4.3.tgz",
@@ -1046,6 +1348,86 @@
         "node": ">=6"
       }
     },
+    "node_modules/dom-serializer": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/dom-serializer/-/dom-serializer-2.0.0.tgz",
+      "integrity": "sha512-wIkAryiqt/nV5EQKqQpo3SToSOV9J0DnbJqwK7Wv/Trc92zIAYZ4FlMu+JPFW1DfGFt81ZTCGgDEabffXeLyJg==",
+      "license": "MIT",
+      "dependencies": {
+        "domelementtype": "^2.3.0",
+        "domhandler": "^5.0.2",
+        "entities": "^4.2.0"
+      },
+      "funding": {
+        "url": "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/cheeriojs/dom-serializer?sponsor=1"
+      }
+    },
+    "node_modules/domelementtype": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/domelementtype/-/domelementtype-2.3.0.tgz",
+      "integrity": "sha512-OLETBj6w0OsagBwdXnPdN0cnMfF9opN69co+7ZrbfPGrdpPVNBUj02spi6B1N7wChLQiPn4CSH/zJvXw56gmHw==",
+      "funding": [
+        {
+          "type": "github",
+          "url": "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/sponsors/fb55"
+        }
+      ],
+      "license": "BSD-2-Clause"
+    },
+    "node_modules/domhandler": {
+      "version": "5.0.3",
+      "resolved": "https://registry.npmjs.org/domhandler/-/domhandler-5.0.3.tgz",
+      "integrity": "sha512-cgwlv/1iFQiFnU96XXgROh8xTeetsnJiDsTc7TYCLFd9+/WNkIqPTxiM/8pSd8VIrhXGTf1Ny1q1hquVqDJB5w==",
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "domelementtype": "^2.3.0"
+      },
+      "engines": {
+        "node": ">= 4"
+      },
+      "funding": {
+        "url": "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/fb55/domhandler?sponsor=1"
+      }
+    },
+    "node_modules/domutils": {
+      "version": "3.2.2",
+      "resolved": "https://registry.npmjs.org/domutils/-/domutils-3.2.2.tgz",
+      "integrity": "sha512-6kZKyUajlDuqlHKVX1w7gyslj9MPIXzIFiz/rGu35uC1wMi+kMhQwGhl4lt9unC9Vb9INnY9Z3/ZA3+FhASLaw==",
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "dom-serializer": "^2.0.0",
+        "domelementtype": "^2.3.0",
+        "domhandler": "^5.0.3"
+      },
+      "funding": {
+        "url": "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/fb55/domutils?sponsor=1"
+      }
+    },
+    "node_modules/encoding-sniffer": {
+      "version": "0.2.1",
+      "resolved": "https://registry.npmjs.org/encoding-sniffer/-/encoding-sniffer-0.2.1.tgz",
+      "integrity": "sha512-5gvq20T6vfpekVtqrYQsSCFZ1wEg5+wW0/QaZMWkFr6BqD3NfKs0rLCx4rrVlSWJeZb5NBJgVLswK/w2MWU+Gw==",
+      "license": "MIT",
+      "dependencies": {
+        "iconv-lite": "^0.6.3",
+        "whatwg-encoding": "^3.1.1"
+      },
+      "funding": {
+        "url": "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/fb55/encoding-sniffer?sponsor=1"
+      }
+    },
+    "node_modules/entities": {
+      "version": "4.5.0",
+      "resolved": "https://registry.npmjs.org/entities/-/entities-4.5.0.tgz",
+      "integrity": "sha512-V0hjH4dGPh9Ao5p0MoRY6BVqtwCjhz6vI5LT8AJ55H+4g9/4vbHx1I54fS0XuclLhDHArPQCiMjDxjaL8fPxhw==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=0.12"
+      },
+      "funding": {
+        "url": "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/fb55/entities?sponsor=1"
+      }
+    },
     "node_modules/es-module-lexer": {
       "version": "1.7.0",
       "resolved": "https://registry.npmjs.org/es-module-lexer/-/es-module-lexer-1.7.0.tgz",
@@ -1149,6 +1531,59 @@
         "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
       }
     },
+    "node_modules/htmlparser2": {
+      "version": "10.1.0",
+      "resolved": "https://registry.npmjs.org/htmlparser2/-/htmlparser2-10.1.0.tgz",
+      "integrity": "sha512-VTZkM9GWRAtEpveh7MSF6SjjrpNVNNVJfFup7xTY3UpFtm67foy9HDVXneLtFVt4pMz5kZtgNcvCniNFb1hlEQ==",
+      "funding": [
+        "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/fb55/htmlparser2?sponsor=1",
+        {
+          "type": "github",
+          "url": "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/sponsors/fb55"
+        }
+      ],
+      "license": "MIT",
+      "dependencies": {
+        "domelementtype": "^2.3.0",
+        "domhandler": "^5.0.3",
+        "domutils": "^3.2.2",
+        "entities": "^7.0.1"
+      }
+    },
+    "node_modules/htmlparser2/node_modules/entities": {
+      "version": "7.0.1",
+      "resolved": "https://registry.npmjs.org/entities/-/entities-7.0.1.tgz",
+      "integrity": "sha512-TWrgLOFUQTH994YUyl1yT4uyavY5nNB5muff+RtWaqNVCAK408b5ZnnbNAUEWLTCpum9w6arT70i1XdQ4UeOPA==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=0.12"
+      },
+      "funding": {
+        "url": "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/fb55/entities?sponsor=1"
+      }
+    },
+    "node_modules/iconv-lite": {
+      "version": "0.6.3",
+      "resolved": "https://registry.npmjs.org/iconv-lite/-/iconv-lite-0.6.3.tgz",
+      "integrity": "sha512-4fCk79wshMdzMp2rH06qWrJE4iolqLhCUH+OiuIgU++RB0+94NlDL81atO7GX55uUKueo0txHNtvEyI6D7WdMw==",
+      "license": "MIT",
+      "dependencies": {
+        "safer-buffer": ">= 2.1.2 < 3.0.0"
+      },
+      "engines": {
+        "node": ">=0.10.0"
+      }
+    },
+    "node_modules/ignore": {
+      "version": "7.0.9",
+      "resolved": "https://registry.npmjs.org/ignore/-/ignore-7.0.9.tgz",
+      "integrity": "sha512-brTTsvFRt5C1gGHtPst/281UjPD5t9fBqbgoMPlVWy11ZLTPfu7HxK4ZYqO9H7o/yC9rSTCI85EaQ4OoY12qYw==",
+      "license": "MIT",
+      "peer": true,
+      "engines": {
+        "node": ">= 4"
+      }
+    },
     "node_modules/js-yaml": {
       "version": "5.4.1",
       "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-5.4.1.tgz",
@@ -1194,6 +1629,44 @@
         "@jridgewell/sourcemap-codec": "^1.5.5"
       }
     },
+    "node_modules/minimatch": {
+      "version": "10.2.6",
+      "resolved": "https://registry.npmjs.org/minimatch/-/minimatch-10.2.6.tgz",
+      "integrity": "sha512-vpLQEs+VLCr1nU0BXS07maYoFwlDAH0gngQuuttxIwutDFEMHq2blX+8vpgxDdK3J1PwjCJiep77OitTZ4Ll1A==",
+      "license": "BlueOak-1.0.0",
+      "dependencies": {
+        "brace-expansion": "^5.0.8"
+      },
+      "engines": {
+        "node": "18 || 20 || >=22"
+      },
+      "funding": {
+        "url": "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/sponsors/isaacs"
+      }
+    },
+    "node_modules/minipass": {
+      "version": "7.1.3",
+      "resolved": "https://registry.npmjs.org/minipass/-/minipass-7.1.3.tgz",
+      "integrity": "sha512-tEBHqDnIoM/1rXME1zgka9g6Q2lcoCkxHLuc7ODJ5BxbP5d4c2Z5cGgtXAku59200Cx7diuHTOYfSBD8n6mm8A==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "engines": {
+        "node": ">=16 || 14 >=14.17"
+      }
+    },
+    "node_modules/minizlib": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/minizlib/-/minizlib-3.1.0.tgz",
+      "integrity": "sha512-KZxYo1BUkWD2TVFLr0MQoM8vUUigWD3LlD83a/75BqC+4qE0Hb1Vo5v1FgcfaNXvfXzr+5EhQ6ing/CaBijTlw==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "minipass": "^7.1.2"
+      },
+      "engines": {
+        "node": ">= 18"
+      }
+    },
     "node_modules/ms": {
       "version": "2.1.3",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
@@ -1220,6 +1693,67 @@
         "node": "^10 || ^12 || ^13.7 || ^14 || >=15.0.1"
       }
     },
+    "node_modules/nth-check": {
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/nth-check/-/nth-check-2.1.1.tgz",
+      "integrity": "sha512-lqjrjmaOoAnWfMmBPL+XNnynZh2+swxiX3WUE0s4yEHI6m+AwrK2UZOimIRl3X/4QctVqS8AiZjFqyOGrMXb/w==",
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "boolbase": "^1.0.0"
+      },
+      "funding": {
+        "url": "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/fb55/nth-check?sponsor=1"
+      }
+    },
+    "node_modules/parse5": {
+      "version": "7.3.0",
+      "resolved": "https://registry.npmjs.org/parse5/-/parse5-7.3.0.tgz",
+      "integrity": "sha512-IInvU7fabl34qmi9gY8XOVxhYyMyuH2xUNpb2q8/Y+7552KlejkRvqvD19nMoUW/uQGGbqNpA6Tufu5FL5BZgw==",
+      "license": "MIT",
+      "dependencies": {
+        "entities": "^6.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5-htmlparser2-tree-adapter": {
+      "version": "7.1.0",
+      "resolved": "https://registry.npmjs.org/parse5-htmlparser2-tree-adapter/-/parse5-htmlparser2-tree-adapter-7.1.0.tgz",
+      "integrity": "sha512-ruw5xyKs6lrpo9x9rCZqZZnIUntICjQAd0Wsmp396Ul9lN/h+ifgVV1x1gZHi8euej6wTfpqX8j+BFQxF0NS/g==",
+      "license": "MIT",
+      "dependencies": {
+        "domhandler": "^5.0.3",
+        "parse5": "^7.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5-parser-stream": {
+      "version": "7.1.2",
+      "resolved": "https://registry.npmjs.org/parse5-parser-stream/-/parse5-parser-stream-7.1.2.tgz",
+      "integrity": "sha512-JyeQc9iwFLn5TbvvqACIF/VXG6abODeB3Fwmv/TGdLk2LfbWkaySGY72at4+Ty7EkPZj854u4CrICqNk2qIbow==",
+      "license": "MIT",
+      "dependencies": {
+        "parse5": "^7.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5/node_modules/entities": {
+      "version": "6.0.1",
+      "resolved": "https://registry.npmjs.org/entities/-/entities-6.0.1.tgz",
+      "integrity": "sha512-aN97NXWF6AWBTahfVOIrB/NShkzi5H7F9r1s9mD3cDj4Ko5f2qhhVoYMibXF7GlLveb/D2ioWay8lxI97Ven3g==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=0.12"
+      },
+      "funding": {
+        "url": "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/fb55/entities?sponsor=1"
+      }
+    },
     "node_modules/pathe": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/pathe/-/pathe-1.1.2.tgz",
@@ -1328,6 +1862,12 @@
         "fsevents": "~2.3.2"
       }
     },
+    "node_modules/safer-buffer": {
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/safer-buffer/-/safer-buffer-2.1.2.tgz",
+      "integrity": "sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg==",
+      "license": "MIT"
+    },
     "node_modules/siginfo": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/siginfo/-/siginfo-2.0.0.tgz",
@@ -1359,6 +1899,23 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/tar": {
+      "version": "7.5.22",
+      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.22.tgz",
+      "integrity": "sha512-MFO/QzvtAOmJbkhOaCTvbGcFN9L9b+JunIsDwaKljSOdcLMea3NJ1k9Usz/rjdfSXTq4dfzfeS7W4p4YOAAHeA==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "dependencies": {
+        "@isaacs/fs-minipass": "^4.0.0",
+        "chownr": "^3.0.0",
+        "minipass": "^7.1.2",
+        "minizlib": "^3.1.0",
+        "yallist": "^5.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/tinybench": {
       "version": "2.9.0",
       "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-2.9.0.tgz",
@@ -1417,6 +1974,15 @@
         "node": ">=14.17"
       }
     },
+    "node_modules/undici": {
+      "version": "7.29.1",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-7.29.1.tgz",
+      "integrity": "sha512-RYONW2MeafgYlkVOKYKkA/Ag7BmXqgIWCa8t1m0JcxrQg9pI9lEqRhAOruOBCbAohOa/gkCF+iPi9hrgvTzu6Q==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=20.18.1"
+      }
+    },
     "node_modules/undici-types": {
       "version": "6.21.0",
       "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-6.21.0.tgz",
@@ -1573,6 +2139,28 @@
         }
       }
     },
+    "node_modules/whatwg-encoding": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/whatwg-encoding/-/whatwg-encoding-3.1.1.tgz",
+      "integrity": "sha512-6qN4hJdMwfYBtE3YBTTHhoeuUrDBPZmbQaxWAqSALV/MeEnR5z1xd8UKud2RAkFoPkmB+hli1TZSnyi84xz1vQ==",
+      "deprecated": "Use @exodus/bytes instead for a more spec-conformant and faster implementation",
+      "license": "MIT",
+      "dependencies": {
+        "iconv-lite": "0.6.3"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/whatwg-mimetype": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/whatwg-mimetype/-/whatwg-mimetype-4.0.0.tgz",
+      "integrity": "sha512-QaKxh0eNIi2mE9p2vEdzfagOKHCcj1pJ56EEHGQOVxp8r9/iszLUUV7v89x9O1p/T+NlTM5W7jW6+cz4Fq1YVg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/why-is-node-running": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/why-is-node-running/-/why-is-node-running-2.3.0.tgz",
@@ -1590,6 +2178,16 @@
         "node": ">=8"
       }
     },
+    "node_modules/yallist": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/yallist/-/yallist-5.0.0.tgz",
+      "integrity": "sha512-YgvUTfwqyc7UXVMrB+SImsVYSmTS8X/tSrtdNZMImM+n7+QTriRXyXim0mBrTXNeqzVF0KWGgHPeiyViFFrNDw==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/yaml": {
       "version": "2.9.0",
       "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.9.0.tgz",
diff --git a/packages/sdk/package.json b/packages/sdk/package.json
index 2d5966718..4d4759075 100644
--- a/packages/sdk/package.json
+++ b/packages/sdk/package.json
@@ -42,6 +42,8 @@
   },
   "license": "Apache-2.0",
   "dependencies": {
+    "@relayfile/adapter-core": "0.5.24",
+    "@relayfile/relay-helpers": "0.4.11",
     "@relayflows/surface": "2.0.8",
     "@types/js-yaml": "^4.0.9",
     "ajv": "^8.17.1",
diff --git a/packages/sdk/src/authored-flow-error.ts b/packages/sdk/src/authored-flow-error.ts
index d68fff3f5..728a24c46 100644
--- a/packages/sdk/src/authored-flow-error.ts
+++ b/packages/sdk/src/authored-flow-error.ts
@@ -4,6 +4,8 @@ import type {
 } from './protocol.js';
 
 export type AuthoredFlowExecutionErrorCode =
+  | 'helper_slack.credential_missing'
+  | 'helper_slack.mount_required'
   | 'agent_cli_unresolved'
   | 'agent_parked'
   | 'llm_cli_unresolved'
diff --git a/packages/sdk/src/authored-flow-executor.ts b/packages/sdk/src/authored-flow-executor.ts
index 23fa7ff18..2b1a54bbd 100644
--- a/packages/sdk/src/authored-flow-executor.ts
+++ b/packages/sdk/src/authored-flow-executor.ts
@@ -1,3 +1,9 @@
+import { randomUUID } from 'node:crypto';
+import { dirname } from 'node:path';
+import { assertSlackCredentials, runSlackEffect } from './authored-slack-effect.js';
+import { checkSlackHelpers } from './slack-preflight.js';
+import { snapshotJsonValue } from './json-value.js';
+import type { SlackCall } from './slack-writeback.js';
 import { authoredWorkerRunner } from './authored-worker-step.js';
 import { readSuccessfulOutput, isSurfaceRunCompletionReason } from './authored-step-output.js';
 import {
@@ -90,6 +96,8 @@ export interface ExecuteAuthoredFlowOptions {
    * `getDefinition` instead; see authored-flow-loader.ts's comment on why.
    */
   readonly getDefinition?: GetFlowDefinition;
+  /** Helper receipt and mock-writeback storage; CLI passes its daemon data directory. */
+  readonly dataDir?: string;
   /**
    * The flow file's own path — passed straight to `checkAuthoredFlow`
    * (cli/check.ts) so `f.agent` resolves a CLI the same way a declarative
@@ -124,7 +132,10 @@ export async function executeAuthoredFlow<Input = undefined>(
     ...(options.onWait !== undefined ? { onWait: options.onWait } : {}),
   };
   const definition = getDefinition<Input>(handle);
-  const headerFields = Object.keys(definition.header);
+  const headerFields = Object.keys(definition.header).filter(key => key !== 'tools');
+  if (definition.header.tools && Object.keys(definition.header.tools).some(key => key !== 'slack')) headerFields.push('tools');
+  const helperPreflight = checkSlackHelpers(definition);
+  if (!helperPreflight.ok) assertSlackCredentials();
   if (headerFields.length > 0) {
     throw new AuthoredFlowExecutionError(
       'unsupported_header',
@@ -176,7 +187,30 @@ export async function executeAuthoredFlow<Input = undefined>(
     ));
   }
 
+  const slackRun = randomUUID();
+  function slackOperation<T>(call: SlackCall): Step<T> {
+    assertOperationAllowed(`slack.${call.verb}`, definition.name, requestedCompletion);
+    const snapshot = snapshotJsonValue(call, 'f.slack call') as unknown as SlackCall;
+    const id = `slack-${slackRun}-${nextStep++}`;
+    return trackStep(authoredSteps, new AuthoredFlowOperation<T>(
+      id, `slack.${call.verb}`,
+      () => assertOperationAllowed(`slack.${call.verb}`, definition.name, requestedCompletion),
+      async () => {
+        const receipt = await runSlackEffect(journal, definition.name, id, snapshot,
+          options.dataDir ?? dirname(journal.socketPath), journalSteps);
+        return (call.verb === 'react' ? undefined : receipt) as T;
+      },
+      lifecycle,
+    ));
+  }
+
   const context: Ctx = {
+    slack: {
+      post: (channel, text, opts) => slackOperation({ type: 'effect', provider: 'slack', verb: 'post', params: { channel, text, ...(opts === undefined ? {} : { opts }) } }),
+      dm: (user, text) => slackOperation({ type: 'effect', provider: 'slack', verb: 'dm', params: { user, text } }),
+      reply: (channel, threadTs, text) => slackOperation({ type: 'effect', provider: 'slack', verb: 'reply', params: { channel, threadTs, text } }),
+      react: (channel, messageTs, emoji) => slackOperation({ type: 'effect', provider: 'slack', verb: 'react', params: { channel, messageTs, emoji } }),
+    },
     run(command) {
       assertOperationAllowed('run', definition.name, requestedCompletion);
       const id = `run-${nextStep++}`;
diff --git a/packages/sdk/src/authored-slack-effect.ts b/packages/sdk/src/authored-slack-effect.ts
new file mode 100644
index 000000000..992fbc6d6
--- /dev/null
+++ b/packages/sdk/src/authored-slack-effect.ts
@@ -0,0 +1,121 @@
+import { existsSync } from 'node:fs';
+import { join } from 'node:path';
+import { randomUUID } from 'node:crypto';
+import { JournalClient } from './journal-client.js';
+import { AuthoredFlowExecutionError } from './authored-flow-error.js';
+import { readCompletedStepOutput } from './authored-step-output.js';
+import type { AuthoredFlowJournalStep } from './authored-flow-executor.js';
+import { compileSpec, toKernelSpec } from './compile.js';
+import { SPEC_SCHEMA_VERSION, type KernelAgentStep } from './spec.js';
+import type { StepDispatchEvent } from './protocol.js';
+import { withWorkerLease } from './worker-lease.js';
+import { checkSlackHelpers } from './slack-preflight.js';
+import { atomicJson, readSlackReceipt, receiptPath, slackWriteback, type SlackCall } from './slack-writeback.js';
+
+export function assertSlackCredentials(): void {
+  const report = checkSlackHelpers({ header: { tools: { slack: true } }, body() {} });
+  if (!report.ok) {
+    const diagnostic = report.diagnostics[0]!;
+    throw new AuthoredFlowExecutionError(
+      diagnostic.kind === 'helper_slack.mount_required' ? diagnostic.kind : 'helper_slack.credential_missing', diagnostic.message);
+  }
+}
+
+/** Each helper uses the existing agent lease + effect protocol; no new kernel verb. */
+export async function runSlackEffect(
+  journal: JournalClient, name: string, stepId: string, call: SlackCall,
+  dataDir: string, journalSteps: AuthoredFlowJournalStep[],
+): Promise<unknown> {
+  assertSlackCredentials();
+  const stream = `slack-helper-${randomUUID()}`;
+  const spec = toKernelSpec(compileSpec({
+    version: SPEC_SCHEMA_VERSION, name: `${name}/${stepId}`,
+    steps: [{ id: stepId, type: 'agent', instruction: JSON.stringify(call),
+      maxIterations: 3, recoveryMode: 'reset',
+      surfaces: { streams: [{ stream }], external: ['/slack'] } }],
+  }));
+  const outcome = await journal.runStart(spec);
+  await atomicJson(join(dataDir, 'helper-runs', `${outcome.run_id}.json`), { provider: 'slack' });
+  await driveSlackEffect(journal, outcome.run_id, spec.steps[0] as KernelAgentStep, call, dataDir);
+  const output = await readCompletedStepOutput(journal, outcome.run_id, stepId, journalSteps);
+  return (output as { receipt: unknown }).receipt;
+}
+
+/** Recognize only the journaled helper envelope, so ordinary agent runs keep their worker path. */
+export async function resumeSlackEffect(journal: JournalClient, runId: string, dataDir: string): Promise<boolean> {
+  if (!/^[A-Za-z0-9_-]+$/.test(runId) || !existsSync(join(dataDir, 'helper-runs', `${runId}.json`))) return false;
+  const entries = (await journal.journalRead(runId, 1)).entries as Array<{
+    entry_type: string; payload: { spec?: { steps?: KernelAgentStep[] } };
+  }>;
+  const steps = entries.find(entry => entry.entry_type === 'run.spawned')?.payload.spec?.steps;
+  if (steps?.length !== 1) return false;
+  const step = steps[0]!;
+  if (step.type !== 'agent' || !step.surfaces?.streams?.[0]?.stream.startsWith('slack-helper-')) return false;
+  const call = JSON.parse(step.instruction) as SlackCall;
+  if (call.type !== 'effect' || call.provider !== 'slack' || !['post', 'dm', 'reply', 'react'].includes(call.verb)) return false;
+  const snapshot = await journal.runGet(runId);
+  if (snapshot.status === 'completed' || snapshot.status === 'failed') return true;
+  assertSlackCredentials();
+  await driveSlackEffect(journal, runId, step, call, dataDir);
+  return true;
+}
+
+async function driveSlackEffect(
+  journal: JournalClient, runId: string, step: KernelAgentStep, call: SlackCall, dataDir: string,
+): Promise<void> {
+  const client = new JournalClient(journal.socketPath);
+  const stream = step.surfaces!.streams![0]!.stream;
+  const pins = { workspace: [], streams: [{ stream, read_offset: 0 }] };
+  let resolve!: () => void;
+  let reject!: (error: unknown) => void;
+  const completed = new Promise<void>((yes, no) => { resolve = yes; reject = no; });
+  // Observe early dispatch failures even while attach/run.resume is still pending.
+  void completed.catch(() => undefined);
+  let executing = false;
+  client.on('step.dispatch', (dispatch: StepDispatchEvent) => {
+    if (executing || dispatch.run_id !== runId || dispatch.step_id !== step.id) return;
+    executing = true;
+    void completeSlackDispatch(client, dispatch, call, dataDir).then(resolve, reject);
+  });
+  client.on('error', reject);
+  try {
+    await client.connect();
+    await client.hello('flows-slack-helper');
+    await client.workerAttach(`slack-${randomUUID()}`, ['agent'], pins, 1);
+    const outcome = await journal.runResume(runId);
+    if (outcome.status === 'completed') return;
+    if (outcome.status === 'failed') {
+      throw new AuthoredFlowExecutionError('step_failed', `Slack helper run ${runId} ${outcome.status}`, undefined, runId);
+    }
+    await completed;
+  } catch (error) {
+    if (error instanceof AuthoredFlowExecutionError) throw error;
+    throw new AuthoredFlowExecutionError('step_failed', error instanceof Error ? error.message : 'Slack effect failed', 'worker_error', runId);
+  } finally { client.close(); }
+}
+
+async function completeSlackDispatch(client: JournalClient, dispatch: StepDispatchEvent, call: SlackCall, dataDir: string): Promise<void> {
+  const output = await withWorkerLease(client, dispatch, async signal => {
+    const file = receiptPath(dataDir, dispatch.run_id, dispatch.step_id);
+    let receipt: unknown;
+    await client.performEffect({
+      runId: dispatch.run_id, stepId: dispatch.step_id, attempt: dispatch.attempt,
+      idempotencyKey: dispatch.idempotency_key, surfacePath: '/slack',
+      revisionBefore: 'pending', revisionAfter: `${dispatch.run_id}:${dispatch.step_id}`,
+    }, async () => {
+      try { receipt = await readSlackReceipt(file); }
+      catch (error) {
+        if ((error as NodeJS.ErrnoException).code !== 'ENOENT') throw error;
+        receipt = await slackWriteback(call, dataDir, dispatch.run_id, dispatch.step_id, signal);
+        await atomicJson(file, receipt);
+      }
+      signal.throwIfAborted();
+    });
+    // Also required after a confirmed election followed by a crash before step.complete.
+    if (receipt === undefined) receipt = await readSlackReceipt(file);
+    return { ...call, idempotencyKey: `${dispatch.run_id}:${dispatch.step_id}`, receipt };
+  });
+  await client.stepComplete(dispatch.run_id, dispatch.step_id, dispatch.attempt,
+    dispatch.idempotency_key, 'success', { output, started_pins: dispatch.pins, end_pins: dispatch.pins,
+      effects: [{ surface_path: '/slack', idempotency_key: dispatch.idempotency_key }] });
+}
diff --git a/packages/sdk/src/cli.ts b/packages/sdk/src/cli.ts
index 4458b515a..47e5d6ea6 100644
--- a/packages/sdk/src/cli.ts
+++ b/packages/sdk/src/cli.ts
@@ -1,4 +1,5 @@
 #!/usr/bin/env node
+import { checkHelperBody } from './cli/check-helper-body.js';
 
 import { renderProgress, type ProgressEvent } from './progress.js';
 import { realpathSync } from 'node:fs';
@@ -97,7 +98,8 @@ export async function runCli(
     // refuses `--data-dir` on `check`, so there is no data dir to attach to.
     // `flows check` keeps working with no daemon, no relayflowd binary and no
     // data directory at all -- a property worth keeping, not an omission.
-    const checked = checkFlow(parsed.value);
+    const checked = /\.(?:[cm]?[jt]s)$/.test(parsed.value)
+      ? await checkHelperBody(parsed.value) : checkFlow(parsed.value);
     emitCheckReport(checked.report, parsed.json, io);
     return checked.report.ok ? 0 : 2;
   }
diff --git a/packages/sdk/src/cli/check-helper-body.ts b/packages/sdk/src/cli/check-helper-body.ts
new file mode 100644
index 000000000..febc5dcde
--- /dev/null
+++ b/packages/sdk/src/cli/check-helper-body.ts
@@ -0,0 +1,14 @@
+import { loadAuthoredFlow } from '../authored-flow-loader.js';
+import { checkSlackHelpers } from '../slack-preflight.js';
+import { inputFailureReport, type CheckExecution } from './check.js';
+
+/** Imports the definition, but never executes arbitrary authored body code. */
+export async function checkHelperBody(path: string): Promise<CheckExecution> {
+  try {
+    const { handle, getDefinition } = await loadAuthoredFlow(path);
+    return { report: { ...checkSlackHelpers(getDefinition(handle)), path } };
+  } catch (error) {
+    return { report: inputFailureReport({ kind: 'invalid_spec',
+      message: error instanceof Error ? error.message : 'Could not import authored flow.' }, path) };
+  }
+}
diff --git a/packages/sdk/src/cli/direct-run.ts b/packages/sdk/src/cli/direct-run.ts
index 1762d1741..3f22d9f12 100644
--- a/packages/sdk/src/cli/direct-run.ts
+++ b/packages/sdk/src/cli/direct-run.ts
@@ -64,6 +64,7 @@ export async function runDirectFlow(
     }
     const result = await executeAuthoredFlow(handle, client, input, {
       getDefinition,
+      dataDir,
       flowPath: path,
       onProgress: options.onProgress,
       localAgentStream: localAgent?.stream,
@@ -105,7 +106,9 @@ export async function runDirectFlow(
     // the same limitation already documented elsewhere).
     if (error instanceof AuthoredFlowLoadError
       || (error instanceof AuthoredFlowExecutionError
-        && (error.code === 'unsupported_header'
+        && (error.code === 'helper_slack.credential_missing'
+          || error.code === 'helper_slack.mount_required'
+          || error.code === 'unsupported_header'
           || error.code === 'agent_cli_unresolved'
           || error.code === 'llm_cli_unresolved'
           || error.code === 'unsupported_workspace_permission'))) {
@@ -113,7 +116,7 @@ export async function runDirectFlow(
         exitCode: 2,
         report: {
           ...fromCheckReport('run', inputFailureReport({
-            kind: 'invalid_spec',
+            kind: error instanceof AuthoredFlowExecutionError && (error.code === 'helper_slack.credential_missing' || error.code === 'helper_slack.mount_required') ? error.code : 'invalid_spec',
             message: error.message,
           }, path)),
           socketPath,
diff --git a/packages/sdk/src/cli/run.ts b/packages/sdk/src/cli/run.ts
index a3ca7356f..495d63486 100644
--- a/packages/sdk/src/cli/run.ts
+++ b/packages/sdk/src/cli/run.ts
@@ -1,3 +1,5 @@
+import { resumeSlackEffect } from '../authored-slack-effect.js';
+import { AuthoredFlowExecutionError } from '../authored-flow-error.js';
 import { join, resolve } from 'node:path';
 import type { ProgressEvent } from '../progress.js';
 import { toKernelSpec } from '../compile.js';
@@ -128,9 +130,15 @@ export async function resumeFlow(
   if (connected !== undefined) return connected;
 
   try {
+    await resumeSlackEffect(client, runId, dataDir);
     const outcome = await client.runResume(runId);
     return await classifyOutcome(client, 'resume', outcome, base, socketPath, options);
   } catch (error) {
+    if (error instanceof AuthoredFlowExecutionError
+      && (error.code === 'helper_slack.credential_missing' || error.code === 'helper_slack.mount_required')) {
+      return { exitCode: 2, report: { ...base, runId, socketPath,
+        diagnostics: [{ severity: 'refusal', kind: error.code, message: error.message }] } };
+    }
     if (!(error instanceof JournalProtocolError) || error.code !== 'run_not_found') {
       return protocolFailure('resume', base, socketPath, error, runId);
     }
diff --git a/packages/sdk/src/failure-kinds.ts b/packages/sdk/src/failure-kinds.ts
index 6eec36b84..fbb2b7139 100644
--- a/packages/sdk/src/failure-kinds.ts
+++ b/packages/sdk/src/failure-kinds.ts
@@ -2,6 +2,8 @@ const SHARED_SPEC_FAILURE_KINDS = ['invalid_spec'] as const;
 
 /** Environment refusal kinds produced after spec validation succeeds. */
 const PREFLIGHT_ENVIRONMENT_FAILURE_KINDS = [
+  'helper_slack.credential_missing',
+  'helper_slack.mount_required',
   'cli_missing',
   'cli_unauthenticated',
   'cli_unresolved',
diff --git a/packages/sdk/src/index.ts b/packages/sdk/src/index.ts
index 64decefed..d29b5324d 100644
--- a/packages/sdk/src/index.ts
+++ b/packages/sdk/src/index.ts
@@ -70,6 +70,7 @@ export {
 } from './authored-flow.js';
 export {
   preflight,
+  preflightHelpers,
   type CliResolution,
   type CliResolutionSource,
   type CliProbeResult,
diff --git a/packages/sdk/src/journal-client.ts b/packages/sdk/src/journal-client.ts
index ff6aeb184..e85ac6d2f 100644
--- a/packages/sdk/src/journal-client.ts
+++ b/packages/sdk/src/journal-client.ts
@@ -65,7 +65,7 @@ export class JournalClient extends EventEmitter {
   private readonly connectTimeoutMs: number;
 
   constructor(
-    private readonly socketPath: string,
+    readonly socketPath: string,
     options: JournalClientOptions = {},
   ) {
     super();
diff --git a/packages/sdk/src/preflight.ts b/packages/sdk/src/preflight.ts
index 30169f196..8b0b38436 100644
--- a/packages/sdk/src/preflight.ts
+++ b/packages/sdk/src/preflight.ts
@@ -490,3 +490,21 @@ function firstCommandWord(command: string): string | undefined {
   const match = rest.match(/^(?:"([^"]+)"|'([^']+)'|([^\s]+))/);
   return match?.[1] ?? match?.[2] ?? match?.[3];
 }
+
+/** Helper preflight never evaluates the authored body. Dynamic uses are checked at call time. */
+export function preflightHelpers(
+  definition: { header: { tools?: { slack?: boolean } }; body: Function },
+  facts: { slackToken?: string; slackMount: boolean; slackMock: boolean },
+): PreflightResult {
+  const usesSlack = definition.header.tools?.slack === true
+    || /(?:\.\s*slack\b|\[\s*['"]slack['"]\s*\])/.test(Function.prototype.toString.call(definition.body));
+  const diagnostics: PreflightDiagnostic[] = usesSlack && !facts.slackMock
+    && !facts.slackToken?.trim() && !facts.slackMount
+    ? [{ severity: 'refusal', kind: 'helper_slack.credential_missing',
+        message: 'f.slack requires SLACK_BOT_TOKEN or a relayfile Slack mount.' }]
+    : usesSlack && !facts.slackMock && !facts.slackMount
+      ? [{ severity: 'refusal', kind: 'helper_slack.mount_required',
+          message: 'f.slack direct bot-token transport is not implemented; configure a relayfile Slack mount.' }]
+      : [];
+  return { ok: diagnostics.length === 0, gates: [], resolutions: [], diagnostics };
+}
diff --git a/packages/sdk/src/slack-preflight.ts b/packages/sdk/src/slack-preflight.ts
new file mode 100644
index 000000000..18a7e0cd7
--- /dev/null
+++ b/packages/sdk/src/slack-preflight.ts
@@ -0,0 +1,19 @@
+import { statSync } from 'node:fs';
+import { join } from 'node:path';
+import { preflightHelpers } from './preflight.js';
+
+export function slackMount(env: NodeJS.ProcessEnv = process.env): string | undefined {
+  const root = [env.RELAYFILE_MOUNT_PATH, env.WORKSPACE_ROOT, env.WORKFORCE_SANDBOX_ROOT,
+    env.RELAYFILE_MOUNT_ROOT, env.RELAYFILE_ROOT].find(value => value?.trim());
+  if (!root?.trim()) return undefined;
+  try { return statSync(join(root, 'slack')).isDirectory() ? root : undefined; }
+  catch { return undefined; }
+}
+
+export function checkSlackHelpers(definition: Parameters<typeof preflightHelpers>[0]) {
+  return preflightHelpers(definition, {
+    slackToken: process.env.SLACK_BOT_TOKEN,
+    slackMount: slackMount() !== undefined,
+    slackMock: process.env.RELAYFLOWS_SLACK_MOCK === '1',
+  });
+}
diff --git a/packages/sdk/src/slack-writeback.ts b/packages/sdk/src/slack-writeback.ts
new file mode 100644
index 000000000..63983a14c
--- /dev/null
+++ b/packages/sdk/src/slack-writeback.ts
@@ -0,0 +1,78 @@
+import { createHash, randomUUID } from 'node:crypto';
+import { mkdir, open, readFile, rename } from 'node:fs/promises';
+import { dirname, join } from 'node:path';
+import { slackClient } from '@relayfile/relay-helpers';
+import { flowRunWritebackIdempotency } from '@relayflows/surface';
+import type { RelayTransport } from '@relayfile/relay-helpers/transport';
+import { writeJsonFile, type WritebackResult } from '@relayfile/adapter-core/vfs-client';
+import { slackMount } from './slack-preflight.js';
+
+export type SlackCall =
+  | { type: 'effect'; provider: 'slack'; verb: 'post'; params: { channel: string; text: string; opts?: { replyTo?: string } } }
+  | { type: 'effect'; provider: 'slack'; verb: 'dm'; params: { user: string; text: string } }
+  | { type: 'effect'; provider: 'slack'; verb: 'reply'; params: { channel: string; threadTs: string; text: string } }
+  | { type: 'effect'; provider: 'slack'; verb: 'react'; params: { channel: string; messageTs: string; emoji: string } };
+
+/** Durable receipt precedes effect.confirm, so a confirmed replay can recover it. */
+export async function atomicJson(path: string, value: unknown): Promise<void> {
+  await mkdir(dirname(path), { recursive: true });
+  const temporary = `${path}.${randomUUID()}.tmp`;
+  const file = await open(temporary, 'wx', 0o600);
+  try { await file.writeFile(JSON.stringify(value)); await file.sync(); }
+  finally { await file.close(); }
+  await rename(temporary, path);
+  const directory = await open(dirname(path), 'r');
+  try { await directory.sync(); } finally { await directory.close(); }
+}
+
+export function receiptPath(dataDir: string, runId: string, stepId: string): string {
+  return join(dataDir, 'helper-receipts', createHash('sha256').update(`${runId}:${stepId}`).digest('hex') + '.json');
+}
+
+export async function slackWriteback(
+  call: SlackCall, dataDir: string, runId: string, stepId: string, signal: AbortSignal,
+): Promise<unknown> {
+  const idempotencyKey = flowRunWritebackIdempotency(runId, stepId);
+  let deliveredRef = '';
+  const transport: RelayTransport = {
+    async read() { throw new Error('Slack effect transport is write-only'); },
+    async list() { throw new Error('Slack effect transport is write-only'); },
+    async write(request) {
+      signal.throwIfAborted();
+      const body: Record<string, unknown> = { ...request.body as Record<string, unknown>, idempotencyKey };
+      const stamped = { ...request, body };
+      const draft = `${request.path}/draft-${createHash('sha256').update(idempotencyKey).digest('hex')}.json`;
+      if (process.env.RELAYFLOWS_SLACK_MOCK === '1') {
+        const ts = `mock-${stepId}`;
+        deliveredRef = `mock-ref-${stepId}`;
+        const result: WritebackResult = { path: deliveredRef, absolutePath: draft, deliveryStatus: 'confirmed', receipt: { externalId: ts } };
+        await atomicJson(join(dataDir, 'mock-writeback', 'slack', `${stepId}.json`), {
+          ...call, ...body, channel: request.parameters.channelId,
+          ...(body.parentRef === undefined ? {} : { replyTo: body.parentRef }),
+          runId, stepId, request: stamped, receipt: result.receipt,
+        });
+        return result;
+      }
+      const mount = slackMount();
+      if (mount !== undefined) {
+        const result = await writeJsonFile({ relayfileMountRoot: mount }, 'slack', `write.${request.resource}`, draft, body);
+        if (result.deliveryStatus !== 'confirmed' || !result.receipt) throw new Error('Slack writeback is pending; no delivery receipt');
+        if (call.verb !== 'react' && !result.receipt.externalId && !result.receipt.ts) throw new Error('Slack writeback has no delivered timestamp');
+        deliveredRef = result.path;
+        return result;
+      }
+      throw new Error('Slack effect requires a relayfile mount; direct bot-token transport is not implemented');
+    },
+  };
+  const client = slackClient({ transport });
+  switch (call.verb) {
+    case 'post': return client.post(call.params.channel, call.params.text, call.params.opts);
+    case 'dm': return client.dm(call.params.user, call.params.text);
+    case 'reply': return { ...await client.reply(call.params.channel, call.params.threadTs, call.params.text), ref: deliveredRef };
+    case 'react': await client.react(call.params.channel, call.params.messageTs, call.params.emoji); return null;
+  }
+}
+
+export async function readSlackReceipt(path: string): Promise<unknown> {
+  return JSON.parse(await readFile(path, 'utf8')) as unknown;
+}
diff --git a/packages/sdk/tests/authored-flow-slack.test.ts b/packages/sdk/tests/authored-flow-slack.test.ts
new file mode 100644
index 000000000..d4250cf34
--- /dev/null
+++ b/packages/sdk/tests/authored-flow-slack.test.ts
@@ -0,0 +1,186 @@
+import { spawn, spawnSync, type ChildProcess } from 'node:child_process';
+import { once } from 'node:events';
+import { existsSync, mkdirSync, symlinkSync, mkdtempSync, readdirSync, readFileSync, realpathSync, rmSync, writeFileSync } from 'node:fs';
+import { homedir, tmpdir } from 'node:os';
+import { dirname, join, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { flow } from '@relayflows/surface';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { executeAuthoredFlow } from '../src/authored-flow-executor.js';
+import { JournalClient } from '../src/journal-client.js';
+import { socketPathFor } from '../src/daemon-connection.js';
+import { resumeFlow } from '../src/cli/run.js';
+import { runCli } from '../src/cli.js';
+import { preflightHelpers } from '../src/preflight.js';
+
+const root = resolve(dirname(fileURLToPath(import.meta.url)), '../../..');
+// Match ops/cargo.sh's per-worktree build output for a plain `npm test` too.
+const worktreeKey = spawnSync('cksum', { input: realpathSync(root), encoding: 'utf8' }).stdout.trim().split(' ')[0]!;
+const target = process.env.CARGO_TARGET_DIR ?? join(process.env.RELAYFLOWS_TOOLCHAIN_HOME ?? join(homedir(), '.relayflows-toolchain'), 'target', worktreeKey);
+const binary = process.env.RELAYFLOWD_BIN ?? join(target, 'debug/relayflowd');
+const directories: string[] = [];
+const children: ChildProcess[] = [];
+const clients: JournalClient[] = [];
+const delay = (ms: number) => new Promise(resolve => setTimeout(resolve, ms));
+
+afterEach(async () => {
+  for (const client of clients.splice(0)) client.close();
+  for (const child of children.splice(0)) await kill(child);
+  for (const dir of directories.splice(0)) rmSync(dir, { recursive: true, force: true });
+  vi.unstubAllEnvs();
+  vi.restoreAllMocks();
+});
+
+function temporary(): string {
+  const dir = mkdtempSync(join(tmpdir(), 'f-slack-'));
+  directories.push(dir);
+  return dir;
+}
+
+async function kill(child: ChildProcess): Promise<void> {
+  if (child.exitCode !== null || child.signalCode !== null) return;
+  const exited = once(child, 'exit');
+  child.kill('SIGKILL');
+  await exited;
+}
+
+async function start(dataDir: string): Promise<{ daemon: ChildProcess; client: JournalClient }> {
+  expect(existsSync(binary), `Build relayflowd first: ${binary}`).toBe(true);
+  const daemon = spawn(binary, ['--data-dir', dataDir, 'serve'], { stdio: ['ignore', 'pipe', 'pipe'] });
+  children.push(daemon);
+  let stderr = '';
+  daemon.stderr!.on('data', chunk => { stderr += String(chunk); });
+  for (let attempt = 0; attempt < 100; attempt++) {
+    const client = new JournalClient(socketPathFor(dataDir), { connectTimeoutMs: 100 });
+    try {
+      await client.connect(); await client.hello('slack-test'); clients.push(client);
+      return { daemon, client };
+    } catch { client.close(); }
+    if (daemon.exitCode !== null) throw new Error(stderr);
+    await delay(20);
+  }
+  throw new Error(`Daemon did not start: ${stderr}`);
+}
+
+function mockFiles(dataDir: string): string[] {
+  return readdirSync(join(dataDir, 'mock-writeback/slack')).filter(file => file.endsWith('.json'));
+}
+
+describe('authored Slack helper effects', () => {
+  it('journals exactly one effect with the authored params and typed receipt, without network', async () => {
+    vi.stubEnv('RELAYFLOWS_SLACK_MOCK', '1');
+    const network = vi.spyOn(globalThis, 'fetch').mockRejectedValue(new Error('network forbidden'));
+    const dataDir = temporary();
+    const { client } = await start(dataDir);
+    const result = await executeAuthoredFlow(flow('slack-post', async f => {
+      const receipt = await f.slack.post('#test', 'hi');
+      expect(receipt).toMatchObject({ channel: '#test', ts: expect.stringMatching(/^mock-slack-/), ref: expect.stringMatching(/^mock-ref-/) });
+      f.done('success');
+    }), client, undefined, { dataDir });
+    const step = result.journalSteps[0]!;
+    const entries = (await client.journalRead(step.runId, 1)).entries as any[];
+    const completed = entries.filter(entry => entry.entry_type === 'step.completed');
+    expect(completed).toHaveLength(1);
+    expect(completed[0]).toMatchObject({ step_id: step.id, payload: { completionReason: 'success', output: {
+      type: 'effect', provider: 'slack', verb: 'post', params: { channel: '#test', text: 'hi' },
+      idempotencyKey: `${step.runId}:${step.id}`, receipt: { channel: '#test', ts: expect.any(String), ref: expect.any(String) },
+    } } });
+    expect(entries.filter(entry => entry.entry_type === 'effect.confirmed')).toHaveLength(1);
+    expect(mockFiles(dataDir)).toEqual([`${step.id}.json`]);
+    expect(network).not.toHaveBeenCalled();
+  });
+
+  it('refuses missing credentials before running the body and flows check exits 2', async () => {
+    for (const key of ['SLACK_BOT_TOKEN', 'RELAYFLOWS_SLACK_MOCK', 'RELAYFILE_MOUNT_PATH', 'WORKSPACE_ROOT', 'WORKFORCE_SANDBOX_ROOT', 'RELAYFILE_MOUNT_ROOT', 'RELAYFILE_ROOT']) vi.stubEnv(key, '');
+    let executed = false;
+    const handle = flow('no-credential', async f => { executed = true; await f.slack.post('#test', 'hi'); f.done('success'); });
+    await expect(executeAuthoredFlow(handle, new JournalClient('/must-not-connect'))).rejects.toMatchObject({ code: 'helper_slack.credential_missing' });
+    expect(executed).toBe(false);
+    const dataDir = temporary();
+    mkdirSync(join(dataDir, 'node_modules/@relayflows'), { recursive: true });
+    symlinkSync(join(root, 'packages/sdk/node_modules/@relayflows/surface'), join(dataDir, 'node_modules/@relayflows/surface'));
+    const fixture = join(dataDir, 'slack.mjs');
+    writeFileSync(fixture, `import { flow } from ${JSON.stringify(join(root, 'packages/sdk/node_modules/@relayflows/surface/dist/index.js'))};\nexport default flow('slack', async f => { await f.slack.post('#test', 'hi'); f.done('success'); });`);
+    const output: string[] = [];
+    expect(await runCli(['check', '--json', fixture], { stdout: line => output.push(line), stderr: line => output.push(line) })).toBe(2);
+    expect(output.join('')).toContain('helper_slack.credential_missing');
+    vi.stubEnv('SLACK_BOT_TOKEN', 'configured-token');
+    await expect(executeAuthoredFlow(handle, new JournalClient('/must-not-connect'))).rejects.toMatchObject({ code: 'helper_slack.mount_required' });
+    expect(executed).toBe(false);
+    expect(preflightHelpers({ header: {}, body: async (f: any) => f.slack.post('#test', 'hi') }, {
+      slackMount: true, slackMock: false,
+    }).ok).toBe(true);
+  });
+
+  it.each(['confirm', 'complete'] as const)('replays after SIGKILL before %s with the same token and one successful completion', async boundary => {
+    vi.stubEnv('RELAYFLOWS_SLACK_MOCK', '1');
+    const dataDir = temporary();
+    const first = await start(dataDir);
+    const script = join(dataDir, 'crash.mjs');
+    writeFileSync(script, `
+      import { flow } from ${JSON.stringify(join(root, 'packages/sdk/node_modules/@relayflows/surface/dist/index.js'))};
+      import { JournalClient } from ${JSON.stringify(join(root, 'packages/sdk/dist/journal-client.js'))};
+      import { executeAuthoredFlow } from ${JSON.stringify(join(root, 'packages/sdk/dist/authored-flow-executor.js'))};
+      JournalClient.prototype.${boundary === 'confirm' ? 'effectConfirm' : 'stepComplete'} = async function() { process.stdout.write('CRASH_BOUNDARY\\n'); await new Promise(() => {}); };
+      const client = new JournalClient(${JSON.stringify(socketPathFor(dataDir))});
+      await client.connect(); await client.hello('crash-child');
+      await executeAuthoredFlow(flow('crash-slack', async f => { await f.slack.post('#test', 'hi'); f.done('success'); }), client, undefined, { dataDir: ${JSON.stringify(dataDir)} });
+    `);
+    const child = spawn(process.execPath, [script], { stdio: ['ignore', 'pipe', 'pipe'] });
+    children.push(child);
+    await new Promise<void>((resolve, reject) => {
+      const timer = setTimeout(() => reject(new Error('Did not reach crash window')), 10_000);
+      child.stdout!.on('data', chunk => { if (String(chunk).includes('CRASH_BOUNDARY')) { clearTimeout(timer); resolve(); } });
+      child.stderr!.on('data', chunk => { clearTimeout(timer); reject(new Error(String(chunk))); });
+    });
+    const file = join(dataDir, 'mock-writeback/slack', mockFiles(dataDir)[0]!);
+    const before = JSON.parse(readFileSync(file, 'utf8'));
+    await kill(child); first.client.close(); await kill(first.daemon);
+    const second = await start(dataDir);
+    // Unconfirmed: lose the cache too to prove the provider token is stable.
+    // Confirmed: the persisted receipt must suffice without another provider write.
+    if (boundary === 'confirm') {
+      for (const cache of readdirSync(join(dataDir, 'helper-receipts'))) rmSync(join(dataDir, 'helper-receipts', cache));
+    }
+    for (const key of ['SLACK_BOT_TOKEN', 'RELAYFLOWS_SLACK_MOCK', 'RELAYFILE_MOUNT_PATH', 'WORKSPACE_ROOT', 'WORKFORCE_SANDBOX_ROOT', 'RELAYFILE_MOUNT_ROOT', 'RELAYFILE_ROOT']) vi.stubEnv(key, '');
+    const refused = await resumeFlow(before.runId, dataDir, { spawn: false });
+    expect(refused.exitCode).toBe(2);
+    expect(refused.report.diagnostics).toContainEqual(expect.objectContaining({ kind: 'helper_slack.credential_missing' }));
+    vi.stubEnv('RELAYFLOWS_SLACK_MOCK', '1');
+    const resumed = await resumeFlow(before.runId, dataDir, { spawn: false });
+    expect(resumed.exitCode, JSON.stringify(resumed.report)).toBe(0);
+    const after = JSON.parse(readFileSync(file, 'utf8'));
+    expect(after.idempotencyKey).toBe(before.idempotencyKey);
+    expect(after.receipt).toEqual(before.receipt);
+    const entries = (await second.client.journalRead(before.runId, 1)).entries as any[];
+    // The kernel records abandoned attempts as step.completed(crashed); one successful
+    // completion is the exactly-once result, while retaining honest crash history.
+    expect(entries.filter(entry => entry.entry_type === 'step.completed' && entry.payload.completionReason === 'success')).toHaveLength(1);
+    expect(entries.filter(entry => entry.entry_type === 'step.completed' && entry.payload.completionReason === 'crashed')).toHaveLength(1);
+    expect(entries.filter(entry => entry.entry_type === 'effect.recorded').length).toBeGreaterThan(1);
+    const again = await resumeFlow(before.runId, dataDir, { spawn: false });
+    expect(again.exitCode).toBe(0);
+    expect(mockFiles(dataDir)).toHaveLength(1);
+  }, 30_000);
+
+  it('writes two files for two calls and supports dm, reply, and react', async () => {
+    vi.stubEnv('RELAYFLOWS_SLACK_MOCK', '1');
+    const dataDir = temporary();
+    const { client } = await start(dataDir);
+    await executeAuthoredFlow(flow('two-posts', async f => {
+      await f.slack.post('#test', 'one'); await f.slack.post('#test', 'two'); f.done('success');
+    }), client, undefined, { dataDir });
+    const files = mockFiles(dataDir);
+    expect(files).toHaveLength(2);
+    expect(new Set(files).size).toBe(2);
+    await executeAuthoredFlow(flow('other-verbs', async f => {
+      expect(await f.slack.dm('U123', 'hello')).toMatchObject({ user: 'U123', ts: expect.any(String) });
+      expect(await f.slack.reply('#test', '123.456', 'reply')).toMatchObject({ channel: '#test', ts: expect.any(String) });
+      expect(await f.slack.react('#test', '123.456', 'thumbsup')).toBeUndefined();
+      f.done('success');
+    }), client, undefined, { dataDir });
+    const captures = mockFiles(dataDir).map(file => JSON.parse(readFileSync(join(dataDir, 'mock-writeback/slack', file), 'utf8')));
+    expect(captures.find(call => call.verb === 'reply').request.body.thread_ts).toBe('123.456');
+    expect(captures.find(call => call.verb === 'react').request.body).toMatchObject({ emoji: 'thumbsup', idempotencyKey: expect.any(String) });
+  });
+});
diff --git a/packages/sdk/tests/preflight.test.ts b/packages/sdk/tests/preflight.test.ts
index 327dce33f..80666bb26 100644
--- a/packages/sdk/tests/preflight.test.ts
+++ b/packages/sdk/tests/preflight.test.ts
@@ -1,3 +1,4 @@
+import { preflightHelpers } from '../src/preflight.js';
 import { describe, expect, it } from 'vitest';
 import {
   PREFLIGHT_FAILURE_KINDS,
@@ -360,6 +361,8 @@ describe('preflight: CLI resolution and refusal predicates', () => {
   // not read as coming from this test alone.
   it('reaches every declared refusal kind, with the converse held by the type', () => {
     const scenarios = [
+      preflightHelpers({ header: { tools: { slack: true } }, body() {} }, { slackMount: false, slackMock: false }),
+      preflightHelpers({ header: { tools: { slack: true } }, body() {} }, { slackToken: 'present', slackMount: false, slackMock: false }),
       preflight({
         version: '0.1.0',
         steps: [{ id: 'a', type: 'deterministic', command: 'x', prompt: 'cross-verb' }],
diff --git a/packages/sdk/tests/slack-writeback.test.ts b/packages/sdk/tests/slack-writeback.test.ts
new file mode 100644
index 000000000..42886543f
--- /dev/null
+++ b/packages/sdk/tests/slack-writeback.test.ts
@@ -0,0 +1,41 @@
+import { mkdtempSync, mkdirSync, readdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { afterEach, expect, it, vi } from 'vitest';
+import { slackWriteback, type SlackCall } from '../src/slack-writeback.js';
+import { slackMount } from '../src/slack-preflight.js';
+
+const dirs: string[] = [];
+afterEach(() => {
+  for (const dir of dirs.splice(0)) rmSync(dir, { recursive: true, force: true });
+  vi.unstubAllEnvs(); vi.restoreAllMocks();
+});
+function setup(): string {
+  for (const key of ['RELAYFLOWS_SLACK_MOCK', 'RELAYFILE_MOUNT_PATH', 'WORKSPACE_ROOT', 'WORKFORCE_SANDBOX_ROOT', 'RELAYFILE_MOUNT_ROOT', 'RELAYFILE_ROOT']) vi.stubEnv(key, '');
+  vi.stubEnv('SLACK_BOT_TOKEN', 'test-token');
+  const dir = mkdtempSync(join(tmpdir(), 'slack-write-')); dirs.push(dir); return dir;
+}
+const post: SlackCall = { type: 'effect', provider: 'slack', verb: 'post', params: { channel: 'C1', text: 'hi' } };
+const signal = () => new AbortController().signal;
+
+it('stamps a real mount draft and waits for its delivered receipt', async () => {
+  const dir = setup();
+  mkdirSync(join(dir, 'slack'));
+  vi.stubEnv('WORKSPACE_ROOT', dir);
+  vi.stubEnv('WORKFORCE_TICK_DELIVERY_ID', 'ambient-tick');
+  expect(slackMount()).toBe(dir); // Empty higher-precedence env must not mask a mount.
+  const network = vi.spyOn(globalThis, 'fetch').mockRejectedValue(new Error('no network'));
+  const request = slackWriteback(post, dir, 'run', 'step', signal());
+  const messages = join(dir, 'slack/channels/C1/messages');
+  let draft: string | undefined;
+  for (let i = 0; i < 100 && !draft; i++) {
+    try { draft = readdirSync(messages).find(file => file.endsWith('.json')); } catch {}
+    if (!draft) await new Promise(resolve => setTimeout(resolve, 10));
+  }
+  expect(draft).toBeDefined();
+  const path = join(messages, draft!);
+  expect(JSON.parse(readFileSync(path, 'utf8'))).toEqual({ text: 'hi', idempotencyKey: 'run:step' });
+  writeFileSync(path, JSON.stringify({ externalId: '123.456' }));
+  expect(await request).toMatchObject({ channel: 'C1', ts: '123.456', ref: expect.any(String) });
+  expect(network).not.toHaveBeenCalled();
+});
diff --git a/packages/surface/bun.lock b/packages/surface/bun.lock
index 3298f4ead..743cefb02 100644
--- a/packages/surface/bun.lock
+++ b/packages/surface/bun.lock
@@ -8,6 +8,9 @@
         "typescript": "^5.6.0",
         "vitest": "^2.1.0",
       },
+      "peerDependencies": {
+        "@relayfile/relay-helpers": "0.4.11",
+      },
     },
   },
   "packages": {
@@ -57,10 +60,32 @@
 
     "@esbuild/win32-x64": ["@esbuild/win32-x64@0.21.5", "", { "os": "win32", "cpu": "x64" }, "sha512-tQd/1efJuzPC6rCFwEvLtci/xNFcTZknmXs98FYDfGE4wP9ClFV98nyKrzJKVPMhdDnjzLhdUyMX4PsQAPjwIw=="],
 
+    "@isaacs/fs-minipass": ["@isaacs/fs-minipass@4.0.1", "", { "dependencies": { "minipass": "^7.0.4" } }, "sha512-wgm9Ehl2jpeqP3zw/7mo3kRHFp5MEDhqAdwy1fTGkHAwnkGOVsgpvQhL8B5n1qlb01jV3n/bI0ZfZp5lWA1k4w=="],
+
     "@jridgewell/sourcemap-codec": ["@jridgewell/sourcemap-codec@1.6.0", "", {}, "sha512-T7jf+5zgsZHwNJ4lvQ7/aezbyk0nNX+zJVWpmHA7VYsEx7a7qr5Rg5IbtJFqkgze5Y2sruq1RUY8Q837Od7iFw=="],
 
     "@napi-rs/lzma-linux-x64-gnu": ["@napi-rs/lzma-linux-x64-gnu@1.5.1", "", { "os": "linux", "cpu": "x64" }, "sha512-oTXEIha4SsuXdTA4Iyskj0kpdx2yVXdhd75c2v3xGrHFfVMsbhTPZU/nMPL4sWKo4pBHm3aucLaqGlF696dTyQ=="],
 
+    "@relayfile/adapter-core": ["@relayfile/adapter-core@0.5.24", "", { "dependencies": { "@scalar/postman-to-openapi": "^0.6.0", "cheerio": "^1.2.0", "minimatch": "^10.0.3", "yaml": "^2.8.1" }, "peerDependencies": { "@relayfile/sdk": ">=0.6.0 <1" }, "bin": { "adapter-core": "dist/src/cli.js" } }, "sha512-bOQRuBoAw2RlYs30RtKsOvXlXzcRx4owhHdj384hPrznBIY3U4ZYcb4pVfzreW9TStHEiX7EguUyqhD9g8DJmA=="],
+
+    "@relayfile/adapter-linear": ["@relayfile/adapter-linear@0.4.12", "", { "dependencies": { "@relayfile/adapter-core": "^0.5.18" }, "peerDependencies": { "@relayfile/sdk": ">=0.6.0 <1" } }, "sha512-obICrTmIkVKXX0vAjGiezOK/cu3iUH6i67fuKLe7Fqcp/Upwrsr70Ap68YxyMvpNOvE4TdbbM1vU+2uGXwM5sg=="],
+
+    "@relayfile/adapter-reddit": ["@relayfile/adapter-reddit@0.2.9", "", { "dependencies": { "@relayfile/adapter-core": "^0.5.15" }, "peerDependencies": { "@relayfile/sdk": ">=0.6.0 <1" } }, "sha512-/ZWkr4SguRRCk4fY6DEtP5NVUHSMWP66GtMou4NJOcf5PaxYSa0ceSVxAN/IcTBG6JqdtbqB4IoWn8V9d/JC3g=="],
+
+    "@relayfile/core": ["@relayfile/core@0.10.57", "", {}, "sha512-oKwNJKGovzdl/6IF3sSVZFsiG2ITH7jXnmFgxbCIYPZ+J7QsQ2zvBhT35sPGiNcD4FfiMpyX9OB8LJXOefNdcQ=="],
+
+    "@relayfile/mount-darwin-arm64": ["@relayfile/mount-darwin-arm64@0.10.57", "", { "os": "darwin", "cpu": "arm64" }, "sha512-yCcjQ7HoCJECnjtZeG7eZwLXa4RAT3RAVAAymdIqKZbMe3wbkF1kg3YNQHuRqYsDEIQzGkA4k5AsITmG1j2PfQ=="],
+
+    "@relayfile/mount-darwin-x64": ["@relayfile/mount-darwin-x64@0.10.57", "", { "os": "darwin", "cpu": "x64" }, "sha512-5Ze1a16Mxc2PTj2Q+AdtRZIMKQ4sxJIIXwPjdWD+9rTMEQeqs7xzSZ1WRIjI89FzyNHBjx/+gzD9FK8Kjuc7Yg=="],
+
+    "@relayfile/mount-linux-arm64": ["@relayfile/mount-linux-arm64@0.10.57", "", { "os": "linux", "cpu": "arm64" }, "sha512-+2MhcDwzb7KSC3qjKWOW+9EnZ8mFKJiVns5fiJwO1oThiAd3CnnCfJzYkbEWRKIL0dH5wg4npdayF23DiBtB5w=="],
+
+    "@relayfile/mount-linux-x64": ["@relayfile/mount-linux-x64@0.10.57", "", { "os": "linux", "cpu": "x64" }, "sha512-Y0OGuGEpglQsUrrR0uzjBzqFyrM8wU5jG1tELJ8LBNhedNUEUupGKD7ixs+i4k9kR8Q68voVsQTfzdgqzW3M+Q=="],
+
+    "@relayfile/relay-helpers": ["@relayfile/relay-helpers@0.4.11", "", { "dependencies": { "@relayfile/adapter-core": "^0.5.15", "@relayfile/adapter-linear": "^0.4.11", "@relayfile/adapter-reddit": "^0.2.9" } }, "sha512-J9S2L+dVRQcxv32BxMq+xEqpBJoG1mNzo1E/CCXY4LYUSl0euZD0ZayaFMcpBhGqx+2IDNiSlGjFun/YQk9OqA=="],
+
+    "@relayfile/sdk": ["@relayfile/sdk@0.10.57", "", { "dependencies": { "@relayfile/core": "0.10.57", "ignore": "^7.0.5", "tar": "^7.5.10" }, "optionalDependencies": { "@relayfile/mount-darwin-arm64": "0.10.57", "@relayfile/mount-darwin-x64": "0.10.57", "@relayfile/mount-linux-arm64": "0.10.57", "@relayfile/mount-linux-x64": "0.10.57" } }, "sha512-9AJIEyyruqVogbdqVfY7q0pjuXJy8IhzxR/1pvwWJiybU1BZO8LFNurlFePTAo/uhLG9cshr0YJRBxv2WbG0Sg=="],
+
     "@rollup/rollup-android-arm-eabi": ["@rollup/rollup-android-arm-eabi@4.63.1", "", { "os": "android", "cpu": "arm" }, "sha512-UZ8sUxPTiHWYX9QNdJedb1kDZSpS1t/VPWBWGSgqHNi9w3Cu6IXvu2mzbhiTiPvtrqgTQJ+zqiAq2iPIPilpaQ=="],
 
     "@rollup/rollup-android-arm64": ["@rollup/rollup-android-arm64@4.63.1", "", { "os": "android", "cpu": "arm64" }, "sha512-cQ4nFQABN5cDvDpbvJ7bMStCpnaVxynZrRMfUJYgxcIk9Sh54FIO1vtfkg0B69REjER77ioZ/ov+eAApx/KmLQ=="],
@@ -111,6 +136,12 @@
 
     "@rollup/rollup-win32-x64-msvc": ["@rollup/rollup-win32-x64-msvc@4.63.1", "", { "os": "win32", "cpu": "x64" }, "sha512-at8QVep6S3h5Y6gSbdGU06bRY5WJkf6WUduM9YtvYMbYhB1MOFfUgc6kehitQXzOtMSaT70q7f9ydPhpqu821w=="],
 
+    "@scalar/helpers": ["@scalar/helpers@0.5.1", "", {}, "sha512-9VvPfv8b+YZVIFwR3SWeq4Y8ij/kU3/kf2M6NKcbf2iVyh63d8s0ssap5m/nOhiz/Puidv/29MAJlJCA0LRssA=="],
+
+    "@scalar/openapi-types": ["@scalar/openapi-types@0.7.0", "", {}, "sha512-kN0PwlJW0de4bwQ4ib+mBHzKJUvBCyR/gwU4zLEq6SCbj+GfgYUh+2a0/yl1WYVUiSkkwFsHjfmQ8KjhR3HK0Q=="],
+
+    "@scalar/postman-to-openapi": ["@scalar/postman-to-openapi@0.6.3", "", { "dependencies": { "@scalar/helpers": "0.5.1", "@scalar/openapi-types": "0.7.0" } }, "sha512-Y/tMuRZG34wEfpTxDfXFp5o2X3ibb5ojGWupGJ9ZxkThCx7rOGydnszJPzEbgDK3eF6nJ6UuE7bCTpIEutYnPw=="],
+
     "@types/estree": ["@types/estree@1.0.9", "", {}, "sha512-GhdPgy1el4/ImP05X05Uw4cw2/M93BCUmnEvWZNStlCzEKME4Fkk+YpoA5OiHNQmoS7Cafb8Xa3Pya8m1Qrzeg=="],
 
     "@vitest/expect": ["@vitest/expect@2.1.9", "", { "dependencies": { "@vitest/spy": "2.1.9", "@vitest/utils": "2.1.9", "chai": "^5.1.2", "tinyrainbow": "^1.2.0" } }, "sha512-UJCIkTBenHeKT1TTlKMJWy1laZewsRIzYighyYiJKZreqtdxSos/S1t+ktRMQWu2CKqaarrkeszJx1cgC5tGZw=="],
@@ -129,16 +160,44 @@
 
     "assertion-error": ["assertion-error@2.0.1", "", {}, "sha512-Izi8RQcffqCeNVgFigKli1ssklIbpHnCYc6AknXGYoB6grJqyeby7jv12JUQgmTAnIDnbck1uxksT4dzN3PWBA=="],
 
+    "balanced-match": ["balanced-match@4.0.4", "", {}, "sha512-BLrgEcRTwX2o6gGxGOCNyMvGSp35YofuYzw9h1IMTRmKqttAZZVU67bdb9Pr2vUHA8+j3i2tJfjO6C6+4myGTA=="],
+
+    "boolbase": ["boolbase@1.0.0", "", {}, "sha512-JZOSA7Mo9sNGB8+UjSgzdLtokWAky1zbztM3WRLCbZ70/3cTANmQmOdR7y2g+J0e2WXywy1yS468tY+IruqEww=="],
+
+    "brace-expansion": ["brace-expansion@5.0.9", "", { "dependencies": { "balanced-match": "^4.0.2" } }, "sha512-ScQ4IuvIEF1TMlP7Zt+vjJ//9zlPb2SDcxWxM3bk8s6t6GGdJ7KO1dCcTidOPJKePW30LE/2cT7wCyPho9/Wxg=="],
+
     "cac": ["cac@6.7.14", "", {}, "sha512-b6Ilus+c3RrdDk+JhLKUAQfzzgLEPy6wcXqS7f/xe1EETvsDP6GORG7SFuOs6cID5YkqchW/LXZbX5bc8j7ZcQ=="],
 
     "chai": ["chai@5.3.3", "", { "dependencies": { "assertion-error": "^2.0.1", "check-error": "^2.1.1", "deep-eql": "^5.0.1", "loupe": "^3.1.0", "pathval": "^2.0.0" } }, "sha512-4zNhdJD/iOjSH0A05ea+Ke6MU5mmpQcbQsSOkgdaUMJ9zTlDTD/GYlwohmIE2u0gaxHYiVHEn1Fw9mZ/ktJWgw=="],
 
     "check-error": ["check-error@2.1.3", "", {}, "sha512-PAJdDJusoxnwm1VwW07VWwUN1sl7smmC3OKggvndJFadxxDRyFJBX/ggnu/KE4kQAB7a3Dp8f/YXC1FlUprWmA=="],
 
+    "cheerio": ["cheerio@1.2.0", "", { "dependencies": { "cheerio-select": "^2.1.0", "dom-serializer": "^2.0.0", "domhandler": "^5.0.3", "domutils": "^3.2.2", "encoding-sniffer": "^0.2.1", "htmlparser2": "^10.1.0", "parse5": "^7.3.0", "parse5-htmlparser2-tree-adapter": "^7.1.0", "parse5-parser-stream": "^7.1.2", "undici": "^7.19.0", "whatwg-mimetype": "^4.0.0" } }, "sha512-WDrybc/gKFpTYQutKIK6UvfcuxijIZfMfXaYm8NMsPQxSYvf+13fXUJ4rztGGbJcBQ/GF55gvrZ0Bc0bj/mqvg=="],
+
+    "cheerio-select": ["cheerio-select@2.1.0", "", { "dependencies": { "boolbase": "^1.0.0", "css-select": "^5.1.0", "css-what": "^6.1.0", "domelementtype": "^2.3.0", "domhandler": "^5.0.3", "domutils": "^3.0.1" } }, "sha512-9v9kG0LvzrlcungtnJtpGNxY+fzECQKhK4EGJX2vByejiMX84MFNQw4UxPJl3bFbTMw+Dfs37XaIkCwTZfLh4g=="],
+
+    "chownr": ["chownr@3.0.0", "", {}, "sha512-+IxzY9BZOQd/XuYPRmrvEVjF/nqj5kgT4kEq7VofrDoM1MxoRjEWkrCC3EtLi59TVawxTAn+orJwFQcrqEN1+g=="],
+
+    "css-select": ["css-select@5.2.2", "", { "dependencies": { "boolbase": "^1.0.0", "css-what": "^6.1.0", "domhandler": "^5.0.2", "domutils": "^3.0.1", "nth-check": "^2.0.1" } }, "sha512-TizTzUddG/xYLA3NXodFM0fSbNizXjOKhqiQQwvhlspadZokn1KDy0NZFS0wuEubIYAV5/c1/lAr0TaaFXEXzw=="],
+
+    "css-what": ["css-what@6.2.2", "", {}, "sha512-u/O3vwbptzhMs3L1fQE82ZSLHQQfto5gyZzwteVIEyeaY5Fc7R4dapF/BvRoSYFeqfBk4m0V1Vafq5Pjv25wvA=="],
+
     "debug": ["debug@4.4.3", "", { "dependencies": { "ms": "^2.1.3" }, "peerDependencies": { "supports-color": "*" }, "optionalPeers": ["supports-color"] }, "sha512-RGwwWnwQvkVfavKVt22FGLw+xYSdzARwm0ru6DhTVA3umU5hZc28V3kO4stgYryrTlLpuvgI9GiijltAjNbcqA=="],
 
     "deep-eql": ["deep-eql@5.0.2", "", {}, "sha512-h5k/5U50IJJFpzfL6nO9jaaumfjO/f2NjK/oYB2Djzm4p9L+3T9qWpZqZ2hAbLPuuYq9wrU08WQyBTL5GbPk5Q=="],
 
+    "dom-serializer": ["dom-serializer@2.0.0", "", { "dependencies": { "domelementtype": "^2.3.0", "domhandler": "^5.0.2", "entities": "^4.2.0" } }, "sha512-wIkAryiqt/nV5EQKqQpo3SToSOV9J0DnbJqwK7Wv/Trc92zIAYZ4FlMu+JPFW1DfGFt81ZTCGgDEabffXeLyJg=="],
+
+    "domelementtype": ["domelementtype@2.3.0", "", {}, "sha512-OLETBj6w0OsagBwdXnPdN0cnMfF9opN69co+7ZrbfPGrdpPVNBUj02spi6B1N7wChLQiPn4CSH/zJvXw56gmHw=="],
+
+    "domhandler": ["domhandler@5.0.3", "", { "dependencies": { "domelementtype": "^2.3.0" } }, "sha512-cgwlv/1iFQiFnU96XXgROh8xTeetsnJiDsTc7TYCLFd9+/WNkIqPTxiM/8pSd8VIrhXGTf1Ny1q1hquVqDJB5w=="],
+
+    "domutils": ["domutils@3.2.2", "", { "dependencies": { "dom-serializer": "^2.0.0", "domelementtype": "^2.3.0", "domhandler": "^5.0.3" } }, "sha512-6kZKyUajlDuqlHKVX1w7gyslj9MPIXzIFiz/rGu35uC1wMi+kMhQwGhl4lt9unC9Vb9INnY9Z3/ZA3+FhASLaw=="],
+
+    "encoding-sniffer": ["encoding-sniffer@0.2.1", "", { "dependencies": { "iconv-lite": "^0.6.3", "whatwg-encoding": "^3.1.1" } }, "sha512-5gvq20T6vfpekVtqrYQsSCFZ1wEg5+wW0/QaZMWkFr6BqD3NfKs0rLCx4rrVlSWJeZb5NBJgVLswK/w2MWU+Gw=="],
+
+    "entities": ["entities@4.5.0", "", {}, "sha512-V0hjH4dGPh9Ao5p0MoRY6BVqtwCjhz6vI5LT8AJ55H+4g9/4vbHx1I54fS0XuclLhDHArPQCiMjDxjaL8fPxhw=="],
+
     "es-module-lexer": ["es-module-lexer@1.7.0", "", {}, "sha512-jEQoCwk8hyb2AZziIOLhDqpm5+2ww5uIE6lkO/6jcOCusfk6LhMHpXXfBLXTZ7Ydyt0j4VoUQv6uGNYbdW+kBA=="],
 
     "esbuild": ["esbuild@0.21.5", "", { "optionalDependencies": { "@esbuild/aix-ppc64": "0.21.5", "@esbuild/android-arm": "0.21.5", "@esbuild/android-arm64": "0.21.5", "@esbuild/android-x64": "0.21.5", "@esbuild/darwin-arm64": "0.21.5", "@esbuild/darwin-x64": "0.21.5", "@esbuild/freebsd-arm64": "0.21.5", "@esbuild/freebsd-x64": "0.21.5", "@esbuild/linux-arm": "0.21.5", "@esbuild/linux-arm64": "0.21.5", "@esbuild/linux-ia32": "0.21.5", "@esbuild/linux-loong64": "0.21.5", "@esbuild/linux-mips64el": "0.21.5", "@esbuild/linux-ppc64": "0.21.5", "@esbuild/linux-riscv64": "0.21.5", "@esbuild/linux-s390x": "0.21.5", "@esbuild/linux-x64": "0.21.5", "@esbuild/netbsd-x64": "0.21.5", "@esbuild/openbsd-x64": "0.21.5", "@esbuild/sunos-x64": "0.21.5", "@esbuild/win32-arm64": "0.21.5", "@esbuild/win32-ia32": "0.21.5", "@esbuild/win32-x64": "0.21.5" }, "bin": { "esbuild": "bin/esbuild" } }, "sha512-mg3OPMV4hXywwpoDxu3Qda5xCKQi+vCTZq8S9J/EpkhB2HzKXq4SNFZE3+NK93JYxc8VMSep+lOUSC/RVKaBqw=="],
@@ -149,14 +208,34 @@
 
     "fsevents": ["fsevents@2.3.3", "", { "os": "darwin" }, "sha512-5xoDfX+fL7faATnagmWPpbFtwh/R77WmMMqqHGS65C3vvB0YHrgF+B1YmZ3441tMj5n63k0212XNoJwzlhffQw=="],
 
+    "htmlparser2": ["htmlparser2@10.1.0", "", { "dependencies": { "domelementtype": "^2.3.0", "domhandler": "^5.0.3", "domutils": "^3.2.2", "entities": "^7.0.1" } }, "sha512-VTZkM9GWRAtEpveh7MSF6SjjrpNVNNVJfFup7xTY3UpFtm67foy9HDVXneLtFVt4pMz5kZtgNcvCniNFb1hlEQ=="],
+
+    "iconv-lite": ["iconv-lite@0.6.3", "", { "dependencies": { "safer-buffer": ">= 2.1.2 < 3.0.0" } }, "sha512-4fCk79wshMdzMp2rH06qWrJE4iolqLhCUH+OiuIgU++RB0+94NlDL81atO7GX55uUKueo0txHNtvEyI6D7WdMw=="],
+
+    "ignore": ["ignore@7.0.9", "", {}, "sha512-brTTsvFRt5C1gGHtPst/281UjPD5t9fBqbgoMPlVWy11ZLTPfu7HxK4ZYqO9H7o/yC9rSTCI85EaQ4OoY12qYw=="],
+
     "loupe": ["loupe@3.2.1", "", {}, "sha512-CdzqowRJCeLU72bHvWqwRBBlLcMEtIvGrlvef74kMnV2AolS9Y8xUv1I0U/MNAWMhBlKIoyuEgoJ0t/bbwHbLQ=="],
 
     "magic-string": ["magic-string@0.30.21", "", { "dependencies": { "@jridgewell/sourcemap-codec": "^1.5.5" } }, "sha512-vd2F4YUyEXKGcLHoq+TEyCjxueSeHnFxyyjNp80yg0XV4vUhnDer/lvvlqM/arB5bXQN5K2/3oinyCRyx8T2CQ=="],
 
+    "minimatch": ["minimatch@10.2.6", "", { "dependencies": { "brace-expansion": "^5.0.8" } }, "sha512-vpLQEs+VLCr1nU0BXS07maYoFwlDAH0gngQuuttxIwutDFEMHq2blX+8vpgxDdK3J1PwjCJiep77OitTZ4Ll1A=="],
+
+    "minipass": ["minipass@7.1.3", "", {}, "sha512-tEBHqDnIoM/1rXME1zgka9g6Q2lcoCkxHLuc7ODJ5BxbP5d4c2Z5cGgtXAku59200Cx7diuHTOYfSBD8n6mm8A=="],
+
+    "minizlib": ["minizlib@3.1.0", "", { "dependencies": { "minipass": "^7.1.2" } }, "sha512-KZxYo1BUkWD2TVFLr0MQoM8vUUigWD3LlD83a/75BqC+4qE0Hb1Vo5v1FgcfaNXvfXzr+5EhQ6ing/CaBijTlw=="],
+
     "ms": ["ms@2.1.3", "", {}, "sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA=="],
 
     "nanoid": ["nanoid@3.3.18", "", { "bin": { "nanoid": "bin/nanoid.cjs" } }, "sha512-DTg4MJbGMWkfi6VZFdNt2/caMbQy4Ou+Op/hJQvGEWcnVfoA1QA+xzRKAzw9jD6+GVOOeYr/mIcuDSdug6F6+w=="],
 
+    "nth-check": ["nth-check@2.1.1", "", { "dependencies": { "boolbase": "^1.0.0" } }, "sha512-lqjrjmaOoAnWfMmBPL+XNnynZh2+swxiX3WUE0s4yEHI6m+AwrK2UZOimIRl3X/4QctVqS8AiZjFqyOGrMXb/w=="],
+
+    "parse5": ["parse5@7.3.0", "", { "dependencies": { "entities": "^6.0.0" } }, "sha512-IInvU7fabl34qmi9gY8XOVxhYyMyuH2xUNpb2q8/Y+7552KlejkRvqvD19nMoUW/uQGGbqNpA6Tufu5FL5BZgw=="],
+
+    "parse5-htmlparser2-tree-adapter": ["parse5-htmlparser2-tree-adapter@7.1.0", "", { "dependencies": { "domhandler": "^5.0.3", "parse5": "^7.0.0" } }, "sha512-ruw5xyKs6lrpo9x9rCZqZZnIUntICjQAd0Wsmp396Ul9lN/h+ifgVV1x1gZHi8euej6wTfpqX8j+BFQxF0NS/g=="],
+
+    "parse5-parser-stream": ["parse5-parser-stream@7.1.2", "", { "dependencies": { "parse5": "^7.0.0" } }, "sha512-JyeQc9iwFLn5TbvvqACIF/VXG6abODeB3Fwmv/TGdLk2LfbWkaySGY72at4+Ty7EkPZj854u4CrICqNk2qIbow=="],
+
     "pathe": ["pathe@1.1.2", "", {}, "sha512-whLdWMYL2TwI08hn8/ZqAbrVemu0LNaNNJZX73O6qaIdCTfXutsLhMkjdENX0qhsQ9uIimo4/aQOmXkoon2nDQ=="],
 
     "pathval": ["pathval@2.0.1", "", {}, "sha512-//nshmD55c46FuFw26xV/xFAaB5HF9Xdap7HJBBnrKdAd6/GxDBaNA1870O79+9ueg61cZLSVc+OaFlfmObYVQ=="],
@@ -167,6 +246,8 @@
 
     "rollup": ["rollup@4.63.1", "", { "dependencies": { "@types/estree": "1.0.9" }, "optionalDependencies": { "@napi-rs/lzma-linux-x64-gnu": "1.5.1", "@rollup/rollup-android-arm-eabi": "4.63.1", "@rollup/rollup-android-arm64": "4.63.1", "@rollup/rollup-darwin-arm64": "4.63.1", "@rollup/rollup-darwin-x64": "4.63.1", "@rollup/rollup-freebsd-arm64": "4.63.1", "@rollup/rollup-freebsd-x64": "4.63.1", "@rollup/rollup-linux-arm-gnueabihf": "4.63.1", "@rollup/rollup-linux-arm-musleabihf": "4.63.1", "@rollup/rollup-linux-arm64-gnu": "4.63.1", "@rollup/rollup-linux-arm64-musl": "4.63.1", "@rollup/rollup-linux-loong64-gnu": "4.63.1", "@rollup/rollup-linux-loong64-musl": "4.63.1", "@rollup/rollup-linux-ppc64-gnu": "4.63.1", "@rollup/rollup-linux-ppc64-musl": "4.63.1", "@rollup/rollup-linux-riscv64-gnu": "4.63.1", "@rollup/rollup-linux-riscv64-musl": "4.63.1", "@rollup/rollup-linux-s390x-gnu": "4.63.1", "@rollup/rollup-linux-x64-gnu": "4.63.1", "@rollup/rollup-linux-x64-musl": "4.63.1", "@rollup/rollup-openbsd-x64": "4.63.1", "@rollup/rollup-openharmony-arm64": "4.63.1", "@rollup/rollup-win32-arm64-msvc": "4.63.1", "@rollup/rollup-win32-ia32-msvc": "4.63.1", "@rollup/rollup-win32-x64-gnu": "4.63.1", "@rollup/rollup-win32-x64-msvc": "4.63.1", "fsevents": "~2.3.2" }, "bin": { "rollup": "dist/bin/rollup" } }, "sha512-3Df9jsstwhccuEfmAMi9l8XUh/GOkVObmFTU7CCVBysEbcOZLl84jCtaAZMcPiMz2EGKsATzQcU+Xr3n/wU6cg=="],
 
+    "safer-buffer": ["safer-buffer@2.1.2", "", {}, "sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg=="],
+
     "siginfo": ["siginfo@2.0.0", "", {}, "sha512-ybx0WO1/8bSBLEWXZvEd7gMW3Sn3JFlW3TvX1nREbDLRNQNaeNN8WK0meBwPdAaOI7TtRRRJn/Es1zhrrCHu7g=="],
 
     "source-map-js": ["source-map-js@1.2.1", "", {}, "sha512-UXWMKhLOwVKb728IUtQPXxfYU+usdybtUrK/8uGE8CQMvrhOpwvzDBwj0QhSL7MQc7vIsISBG8VQ8+IDQxpfQA=="],
@@ -175,6 +256,8 @@
 
     "std-env": ["std-env@3.10.0", "", {}, "sha512-5GS12FdOZNliM5mAOxFRg7Ir0pWz8MdpYm6AY6VPkGpbA7ZzmbzNcBJQ0GPvvyWgcY7QAhCgf9Uy89I03faLkg=="],
 
+    "tar": ["tar@7.5.22", "", { "dependencies": { "@isaacs/fs-minipass": "^4.0.0", "chownr": "^3.0.0", "minipass": "^7.1.2", "minizlib": "^3.1.0", "yallist": "^5.0.0" } }, "sha512-MFO/QzvtAOmJbkhOaCTvbGcFN9L9b+JunIsDwaKljSOdcLMea3NJ1k9Usz/rjdfSXTq4dfzfeS7W4p4YOAAHeA=="],
+
     "tinybench": ["tinybench@2.9.0", "", {}, "sha512-0+DUvqWMValLmha6lr4kD8iAMK1HzV0/aKnCtWb9v9641TnP/MFb7Pc2bxoxQjTXAErryXVgUOfv2YqNllqGeg=="],
 
     "tinyexec": ["tinyexec@0.3.2", "", {}, "sha512-KQQR9yN7R5+OSwaK0XQoj22pwHoTlgYqmUscPYoknOoWCWfj/5/ABTMRi69FrKU5ffPVh5QcFikpWJI/P1ocHA=="],
@@ -187,12 +270,26 @@
 
     "typescript": ["typescript@5.9.3", "", { "bin": { "tsc": "bin/tsc", "tsserver": "bin/tsserver" } }, "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw=="],
 
+    "undici": ["undici@7.29.1", "", {}, "sha512-RYONW2MeafgYlkVOKYKkA/Ag7BmXqgIWCa8t1m0JcxrQg9pI9lEqRhAOruOBCbAohOa/gkCF+iPi9hrgvTzu6Q=="],
+
     "vite": ["vite@5.4.21", "", { "dependencies": { "esbuild": "^0.21.3", "postcss": "^8.4.43", "rollup": "^4.20.0" }, "optionalDependencies": { "fsevents": "~2.3.3" }, "peerDependencies": { "@types/node": "^18.0.0 || >=20.0.0", "less": "*", "lightningcss": "^1.21.0", "sass": "*", "sass-embedded": "*", "stylus": "*", "sugarss": "*", "terser": "^5.4.0" }, "optionalPeers": ["@types/node", "less", "lightningcss", "sass", "sass-embedded", "stylus", "sugarss", "terser"], "bin": { "vite": "bin/vite.js" } }, "sha512-o5a9xKjbtuhY6Bi5S3+HvbRERmouabWbyUcpXXUA1u+GNUKoROi9byOJ8M0nHbHYHkYICiMlqxkg1KkYmm25Sw=="],
 
     "vite-node": ["vite-node@2.1.9", "", { "dependencies": { "cac": "^6.7.14", "debug": "^4.3.7", "es-module-lexer": "^1.5.4", "pathe": "^1.1.2", "vite": "^5.0.0" }, "bin": { "vite-node": "vite-node.mjs" } }, "sha512-AM9aQ/IPrW/6ENLQg3AGY4K1N2TGZdR5e4gu/MmmR2xR3Ll1+dib+nook92g4TV3PXVyeyxdWwtaCAiUL0hMxA=="],
 
     "vitest": ["vitest@2.1.9", "", { "dependencies": { "@vitest/expect": "2.1.9", "@vitest/mocker": "2.1.9", "@vitest/pretty-format": "^2.1.9", "@vitest/runner": "2.1.9", "@vitest/snapshot": "2.1.9", "@vitest/spy": "2.1.9", "@vitest/utils": "2.1.9", "chai": "^5.1.2", "debug": "^4.3.7", "expect-type": "^1.1.0", "magic-string": "^0.30.12", "pathe": "^1.1.2", "std-env": "^3.8.0", "tinybench": "^2.9.0", "tinyexec": "^0.3.1", "tinypool": "^1.0.1", "tinyrainbow": "^1.2.0", "vite": "^5.0.0", "vite-node": "2.1.9", "why-is-node-running": "^2.3.0" }, "peerDependencies": { "@edge-runtime/vm": "*", "@types/node": "^18.0.0 || >=20.0.0", "@vitest/browser": "2.1.9", "@vitest/ui": "2.1.9", "happy-dom": "*", "jsdom": "*" }, "optionalPeers": ["@edge-runtime/vm", "@types/node", "@vitest/browser", "@vitest/ui", "happy-dom", "jsdom"], "bin": { "vitest": "vitest.mjs" } }, "sha512-MSmPM9REYqDGBI8439mA4mWhV5sKmDlBKWIYbA3lRb2PTHACE0mgKwA8yQ2xq9vxDTuk4iPrECBAEW2aoFXY0Q=="],
 
+    "whatwg-encoding": ["whatwg-encoding@3.1.1", "", { "dependencies": { "iconv-lite": "0.6.3" } }, "sha512-6qN4hJdMwfYBtE3YBTTHhoeuUrDBPZmbQaxWAqSALV/MeEnR5z1xd8UKud2RAkFoPkmB+hli1TZSnyi84xz1vQ=="],
+
+    "whatwg-mimetype": ["whatwg-mimetype@4.0.0", "", {}, "sha512-QaKxh0eNIi2mE9p2vEdzfagOKHCcj1pJ56EEHGQOVxp8r9/iszLUUV7v89x9O1p/T+NlTM5W7jW6+cz4Fq1YVg=="],
+
     "why-is-node-running": ["why-is-node-running@2.3.0", "", { "dependencies": { "siginfo": "^2.0.0", "stackback": "0.0.2" }, "bin": { "why-is-node-running": "cli.js" } }, "sha512-hUrmaWBdVDcxvYqnyh09zunKzROWjbZTiNy8dBEjkS7ehEDQibXJ7XvlmtbwuTclUiIyN+CyXQD4Vmko8fNm8w=="],
+
+    "yallist": ["yallist@5.0.0", "", {}, "sha512-YgvUTfwqyc7UXVMrB+SImsVYSmTS8X/tSrtdNZMImM+n7+QTriRXyXim0mBrTXNeqzVF0KWGgHPeiyViFFrNDw=="],
+
+    "yaml": ["yaml@2.9.0", "", { "bin": { "yaml": "bin.mjs" } }, "sha512-2AvhNX3mb8zd6Zy7INTtSpl1F15HW6Wnqj0srWlkKLcpYl/gMIMJiyuGq2KeI2YFxUPjdlB+3Lc10seMLtL4cA=="],
+
+    "htmlparser2/entities": ["entities@7.0.1", "", {}, "sha512-TWrgLOFUQTH994YUyl1yT4uyavY5nNB5muff+RtWaqNVCAK408b5ZnnbNAUEWLTCpum9w6arT70i1XdQ4UeOPA=="],
+
+    "parse5/entities": ["entities@6.0.1", "", {}, "sha512-aN97NXWF6AWBTahfVOIrB/NShkzi5H7F9r1s9mD3cDj4Ko5f2qhhVoYMibXF7GlLveb/D2ioWay8lxI97Ven3g=="],
   }
 }
diff --git a/packages/surface/package-lock.json b/packages/surface/package-lock.json
index ec47c375b..d699ec4a9 100644
--- a/packages/surface/package-lock.json
+++ b/packages/surface/package-lock.json
@@ -14,6 +14,9 @@
       },
       "engines": {
         "node": ">=20.19.0 || >=22.12.0"
+      },
+      "peerDependencies": {
+        "@relayfile/relay-helpers": "0.4.11"
       }
     },
     "node_modules/@esbuild/aix-ppc64": {
@@ -407,6 +410,19 @@
         "node": ">=12"
       }
     },
+    "node_modules/@isaacs/fs-minipass": {
+      "version": "4.0.1",
+      "resolved": "https://registry.npmjs.org/@isaacs/fs-minipass/-/fs-minipass-4.0.1.tgz",
+      "integrity": "sha512-wgm9Ehl2jpeqP3zw/7mo3kRHFp5MEDhqAdwy1fTGkHAwnkGOVsgpvQhL8B5n1qlb01jV3n/bI0ZfZp5lWA1k4w==",
+      "license": "ISC",
+      "peer": true,
+      "dependencies": {
+        "minipass": "^7.0.4"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      }
+    },
     "node_modules/@jridgewell/sourcemap-codec": {
       "version": "1.6.0",
       "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.6.0.tgz",
@@ -434,6 +450,159 @@
         "node": "^22.20 || ^24.12 || >=25"
       }
     },
+    "node_modules/@relayfile/adapter-core": {
+      "version": "0.5.24",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-core/-/adapter-core-0.5.24.tgz",
+      "integrity": "sha512-bOQRuBoAw2RlYs30RtKsOvXlXzcRx4owhHdj384hPrznBIY3U4ZYcb4pVfzreW9TStHEiX7EguUyqhD9g8DJmA==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "dependencies": {
+        "@scalar/postman-to-openapi": "^0.6.0",
+        "cheerio": "^1.2.0",
+        "minimatch": "^10.0.3",
+        "yaml": "^2.8.1"
+      },
+      "bin": {
+        "adapter-core": "dist/src/cli.js"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/adapter-linear": {
+      "version": "0.4.12",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-linear/-/adapter-linear-0.4.12.tgz",
+      "integrity": "sha512-obICrTmIkVKXX0vAjGiezOK/cu3iUH6i67fuKLe7Fqcp/Upwrsr70Ap68YxyMvpNOvE4TdbbM1vU+2uGXwM5sg==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "dependencies": {
+        "@relayfile/adapter-core": "^0.5.18"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/adapter-reddit": {
+      "version": "0.2.9",
+      "resolved": "https://registry.npmjs.org/@relayfile/adapter-reddit/-/adapter-reddit-0.2.9.tgz",
+      "integrity": "sha512-/ZWkr4SguRRCk4fY6DEtP5NVUHSMWP66GtMou4NJOcf5PaxYSa0ceSVxAN/IcTBG6JqdtbqB4IoWn8V9d/JC3g==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "dependencies": {
+        "@relayfile/adapter-core": "^0.5.15"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "peerDependencies": {
+        "@relayfile/sdk": ">=0.6.0 <1"
+      }
+    },
+    "node_modules/@relayfile/core": {
+      "version": "0.10.57",
+      "resolved": "https://registry.npmjs.org/@relayfile/core/-/core-0.10.57.tgz",
+      "integrity": "sha512-oKwNJKGovzdl/6IF3sSVZFsiG2ITH7jXnmFgxbCIYPZ+J7QsQ2zvBhT35sPGiNcD4FfiMpyX9OB8LJXOefNdcQ==",
+      "license": "Apache-2.0",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
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+    "node_modules/nth-check": {
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/nth-check/-/nth-check-2.1.1.tgz",
+      "integrity": "sha512-lqjrjmaOoAnWfMmBPL+XNnynZh2+swxiX3WUE0s4yEHI6m+AwrK2UZOimIRl3X/4QctVqS8AiZjFqyOGrMXb/w==",
+      "license": "BSD-2-Clause",
+      "peer": true,
+      "dependencies": {
+        "boolbase": "^1.0.0"
+      },
+      "funding": {
+        "url": "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/fb55/nth-check?sponsor=1"
+      }
+    },
+    "node_modules/parse5": {
+      "version": "7.3.0",
+      "resolved": "https://registry.npmjs.org/parse5/-/parse5-7.3.0.tgz",
+      "integrity": "sha512-IInvU7fabl34qmi9gY8XOVxhYyMyuH2xUNpb2q8/Y+7552KlejkRvqvD19nMoUW/uQGGbqNpA6Tufu5FL5BZgw==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "entities": "^6.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5-htmlparser2-tree-adapter": {
+      "version": "7.1.0",
+      "resolved": "https://registry.npmjs.org/parse5-htmlparser2-tree-adapter/-/parse5-htmlparser2-tree-adapter-7.1.0.tgz",
+      "integrity": "sha512-ruw5xyKs6lrpo9x9rCZqZZnIUntICjQAd0Wsmp396Ul9lN/h+ifgVV1x1gZHi8euej6wTfpqX8j+BFQxF0NS/g==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "domhandler": "^5.0.3",
+        "parse5": "^7.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5-parser-stream": {
+      "version": "7.1.2",
+      "resolved": "https://registry.npmjs.org/parse5-parser-stream/-/parse5-parser-stream-7.1.2.tgz",
+      "integrity": "sha512-JyeQc9iwFLn5TbvvqACIF/VXG6abODeB3Fwmv/TGdLk2LfbWkaySGY72at4+Ty7EkPZj854u4CrICqNk2qIbow==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "parse5": "^7.0.0"
+      },
+      "funding": {
+        "url": "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/inikulin/parse5?sponsor=1"
+      }
+    },
+    "node_modules/parse5/node_modules/entities": {
+      "version": "6.0.1",
+      "resolved": "https://registry.npmjs.org/entities/-/entities-6.0.1.tgz",
+      "integrity": "sha512-aN97NXWF6AWBTahfVOIrB/NShkzi5H7F9r1s9mD3cDj4Ko5f2qhhVoYMibXF7GlLveb/D2ioWay8lxI97Ven3g==",
+      "license": "BSD-2-Clause",
+      "peer": true,
+      "engines": {
+        "node": ">=0.12"
+      },
+      "funding": {
+        "url": "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/fb55/entities?sponsor=1"
+      }
+    },
     "node_modules/pathe": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/pathe/-/pathe-1.1.2.tgz",
@@ -1241,6 +1805,13 @@
         "fsevents": "~2.3.2"
       }
     },
+    "node_modules/safer-buffer": {
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/safer-buffer/-/safer-buffer-2.1.2.tgz",
+      "integrity": "sha512-YZo3K82SD7Riyi0E1EQPojLz7kpepnSQI9IyPbHHg1XXXevb5dJI7tpyN2ADxGcQbHG7vcyRHk0cbwqcQriUtg==",
+      "license": "MIT",
+      "peer": true
+    },
     "node_modules/siginfo": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/siginfo/-/siginfo-2.0.0.tgz",
@@ -1272,6 +1843,23 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/tar": {
+      "version": "7.5.22",
+      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.22.tgz",
+      "integrity": "sha512-MFO/QzvtAOmJbkhOaCTvbGcFN9L9b+JunIsDwaKljSOdcLMea3NJ1k9Usz/rjdfSXTq4dfzfeS7W4p4YOAAHeA==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "dependencies": {
+        "@isaacs/fs-minipass": "^4.0.0",
+        "chownr": "^3.0.0",
+        "minipass": "^7.1.2",
+        "minizlib": "^3.1.0",
+        "yallist": "^5.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/tinybench": {
       "version": "2.9.0",
       "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-2.9.0.tgz",
@@ -1330,6 +1918,16 @@
         "node": ">=14.17"
       }
     },
+    "node_modules/undici": {
+      "version": "7.29.1",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-7.29.1.tgz",
+      "integrity": "sha512-RYONW2MeafgYlkVOKYKkA/Ag7BmXqgIWCa8t1m0JcxrQg9pI9lEqRhAOruOBCbAohOa/gkCF+iPi9hrgvTzu6Q==",
+      "license": "MIT",
+      "peer": true,
+      "engines": {
+        "node": ">=20.18.1"
+      }
+    },
     "node_modules/vite": {
       "version": "5.4.21",
       "resolved": "https://registry.npmjs.org/vite/-/vite-5.4.21.tgz",
@@ -1479,6 +2077,30 @@
         }
       }
     },
+    "node_modules/whatwg-encoding": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/whatwg-encoding/-/whatwg-encoding-3.1.1.tgz",
+      "integrity": "sha512-6qN4hJdMwfYBtE3YBTTHhoeuUrDBPZmbQaxWAqSALV/MeEnR5z1xd8UKud2RAkFoPkmB+hli1TZSnyi84xz1vQ==",
+      "deprecated": "Use @exodus/bytes instead for a more spec-conformant and faster implementation",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "iconv-lite": "0.6.3"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/whatwg-mimetype": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/whatwg-mimetype/-/whatwg-mimetype-4.0.0.tgz",
+      "integrity": "sha512-QaKxh0eNIi2mE9p2vEdzfagOKHCcj1pJ56EEHGQOVxp8r9/iszLUUV7v89x9O1p/T+NlTM5W7jW6+cz4Fq1YVg==",
+      "license": "MIT",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
+      }
+    },
     "node_modules/why-is-node-running": {
       "version": "2.3.0",
       "resolved": "https://registry.npmjs.org/why-is-node-running/-/why-is-node-running-2.3.0.tgz",
@@ -1495,6 +2117,32 @@
       "engines": {
         "node": ">=8"
       }
+    },
+    "node_modules/yallist": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/yallist/-/yallist-5.0.0.tgz",
+      "integrity": "sha512-YgvUTfwqyc7UXVMrB+SImsVYSmTS8X/tSrtdNZMImM+n7+QTriRXyXim0mBrTXNeqzVF0KWGgHPeiyViFFrNDw==",
+      "license": "BlueOak-1.0.0",
+      "peer": true,
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/yaml": {
+      "version": "2.9.0",
+      "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.9.0.tgz",
+      "integrity": "sha512-2AvhNX3mb8zd6Zy7INTtSpl1F15HW6Wnqj0srWlkKLcpYl/gMIMJiyuGq2KeI2YFxUPjdlB+3Lc10seMLtL4cA==",
+      "license": "ISC",
+      "peer": true,
+      "bin": {
+        "yaml": "bin.mjs"
+      },
+      "engines": {
+        "node": ">= 14.6"
+      },
+      "funding": {
+        "url": "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/sponsors/eemeli"
+      }
     }
   }
 }
diff --git a/packages/surface/package.json b/packages/surface/package.json
index 27ec996fd..9dd8c0854 100644
--- a/packages/surface/package.json
+++ b/packages/surface/package.json
@@ -41,5 +41,8 @@
     "type": "git",
     "url": "git+https://github.com/AgentWorkforce/flows.git",
     "directory": "packages/surface"
+  },
+  "peerDependencies": {
+    "@relayfile/relay-helpers": "0.4.11"
   }
 }
diff --git a/packages/surface/src/context.ts b/packages/surface/src/context.ts
index 2594266f8..69d3229a1 100644
--- a/packages/surface/src/context.ts
+++ b/packages/surface/src/context.ts
@@ -1,3 +1,4 @@
+import type { SlackHelper } from "./slack.js";
 import type { CloudHelper } from "./cloud.js";
 import type { RunCompletionReason } from "./completion.js";
 import type { Step } from "./step.js";
@@ -37,4 +38,5 @@ export interface Ctx {
   dispatch<T>(flow: string, input: unknown): Promise<T>;
   done(reason: RunCompletionReason): void;
   cloud: CloudHelper;
+  slack: SlackHelper;
 }
diff --git a/packages/surface/src/flow.ts b/packages/surface/src/flow.ts
index fa1f358d8..cb0f4a3d5 100644
--- a/packages/surface/src/flow.ts
+++ b/packages/surface/src/flow.ts
@@ -5,7 +5,7 @@ export interface FlowHeader {
   identity?: string;
   memory?: { script?: boolean; agent?: boolean };
   budget?: string;
-  tools?: { relayfile?: string[]; mcp?: string[] };
+  tools?: { slack?: boolean; relayfile?: string[]; mcp?: string[] };
   workspace?: string;
 }
 
@@ -16,6 +16,7 @@ export interface ReadonlyFlowHeader {
   readonly memory?: Readonly<{ script?: boolean; agent?: boolean }>;
   readonly budget?: string;
   readonly tools?: Readonly<{
+    slack?: boolean;
     relayfile?: readonly string[];
     mcp?: readonly string[];
   }>;
@@ -129,6 +130,7 @@ function freezeHeader(header: FlowHeader): ReadonlyFlowHeader {
   const tools = header.tools === undefined
     ? undefined
     : Object.freeze({
+        ...(header.tools.slack === undefined ? {} : { slack: header.tools.slack }),
         ...(header.tools.relayfile === undefined
           ? {}
           : { relayfile: Object.freeze([...header.tools.relayfile]) }),
@@ -172,9 +174,10 @@ function assertFlowHeader(value: unknown, flowName: string): asserts value is Fl
     assertHeaderObject(value.tools, `${at}.tools`);
     assertKnownKeys(
       value.tools,
-      ["relayfile", "mcp"],
+      ["relayfile", "mcp", "slack"],
       `${at}.tools`,
     );
+    assertOptionalBoolean(value.tools, "slack", `${at}.tools`);
     assertOptionalStringArray(value.tools, "relayfile", `${at}.tools`);
     assertOptionalStringArray(value.tools, "mcp", `${at}.tools`);
   }
diff --git a/packages/surface/src/index.ts b/packages/surface/src/index.ts
index 437d99f60..a8409d411 100644
--- a/packages/surface/src/index.ts
+++ b/packages/surface/src/index.ts
@@ -20,3 +20,4 @@ export {
   type FlowHandle,
   type FlowHeader,
 } from "./flow.js";
+export { flowRunWritebackIdempotency, type SlackHelper, type SlackReceipt } from "./slack.js";
diff --git a/packages/surface/src/slack.ts b/packages/surface/src/slack.ts
new file mode 100644
index 000000000..1654d1735
--- /dev/null
+++ b/packages/surface/src/slack.ts
@@ -0,0 +1,20 @@
+import type { Step } from "./step.js";
+
+export interface SlackReceipt {
+  channel: string;
+  ts: string;
+  ref: string;
+}
+
+/** Slack writeback helpers; every call is a journal-backed effect. */
+export interface SlackHelper {
+  post(channel: string, text: string, opts?: { replyTo?: string }): Step<SlackReceipt>;
+  dm(user: string, text: string): Step<{ user: string; ts: string }>;
+  reply(channel: string, threadTs: string, text: string): Step<SlackReceipt>;
+  react(channel: string, messageTs: string, emoji: string): Step<void>;
+}
+
+/** Stable across attempts; deliberately independent of process-tick ordinals. */
+export function flowRunWritebackIdempotency(runId: string, stepId: string): string {
+  return `${runId}:${stepId}`;
+}
diff --git a/scripts/surface-package-gate.sh b/scripts/surface-package-gate.sh
index 1d74d5a06..6be884857 100755
--- a/scripts/surface-package-gate.sh
+++ b/scripts/surface-package-gate.sh
@@ -113,6 +113,8 @@ import {
   type AgentOptions,
   type AgentResult,
   type CloudHelper,
+  type SlackHelper,
+  type SlackReceipt,
   type CompletionReason,
   type Ctx,
   type FlowHandle,
@@ -131,6 +133,10 @@ const body = async (f: Ctx): Promise<void> => {
   const options: AgentOptions = { task: 'review' };
   const agent: Step<AgentResult> = f.agent('reviewer', options);
   await agent;
+  const slack: SlackHelper = f.slack;
+  const post: Step<SlackReceipt> = slack.post('#test', 'hi');
+  await post;
+  await f.slack.post('#test', 'typed');
   f.done('success');
 };
 const header: FlowHeader = { identity: 'packed-type-consumer' };