fix(contracts): a context record that cannot be encoded no longer fails the send

[juliusmarminge]

Follow-up to #16300, from a post-merge review.

Problem

#16300 made ForwardCompatibleArray send an element it cannot encode as a hole, so that one bad element costs only itself. That works for bare arrays such as ServerProviders, where JSON turns the hole into null.

It breaks for message context. OrchestrationMessageContext and ComposerContextClipboardFragment bound their records as Array(Unknown) before forward-compatible decoding. The RPC JSON codec rejects undefined in an Unknown slot, so one context record with a whitespace-only field (for example terminalLabel: " ") made the client's encode fail. RpcClient turns that into a defect, so the whole message send died. Before #16300 the record encoded as "" and only that record was dropped.

No current client produces such a record (web trims and rejects blank terminal labels), so this hasn't happened yet, but it is exactly the case #16300 meant to handle.

Two smaller leftovers from the same change:

• Holes passed type checks. The decoded array type now admitted holes, so Schema.is(ServerProviders)([undefined]) returned true, and Schema.is(OrchestrationMessageContext) threw on a hole instead of returning false.
• One mobile route was missed. The git overview sheet (threads/:environmentId/:threadId/git) still called ThreadId.make on a raw deep-link param, so a hand-typed link with a blank ID reached the screen's error fallback.

Fix

• Holes are dropped before the wire. ForwardCompatibleArray's encode filters them out, so an element that fails its own checks is left out, whatever wraps the array. An element whose encode transformation fails after its checks pass still leaves a hole. No context record can do that, because their encode steps are trims.
• Unknown-kind context payloads must be JSON values. The payload check only required JSON.stringify to succeed. A Date, NaN or undefined field passed it and then failed the whole message's JSON encode. Such a record now fails its own check and is dropped like any other. So is a payload JSON.stringify throws on (a bigint or a cycle, or nesting deeper than the engine's stack, which varies by runtime).
• Optional context record fields are optionalKey. A known record holding an explicit undefined (fenceLanguage: undefined) now fails its own check and is dropped alone, instead of failing the send. Decoding is unchanged: records pass an Array(Unknown) JSON bound before they decode, so null in these fields was already rejected on every real wire path. Producers serialize with JSON.stringify, which omits undefined, so no stored record holds null there. That covers RPC, the SQLite projection and event codecs, the clipboard, the mobile outbox and drafts, and the web prompt stash.
• A decoded array may not contain holes. That puts Schema.is and make back to rejecting [undefined], as before fix(contracts): trimmed IDs round-trip #16300. The check aborts, so the context's contextId uniqueness filter never runs on a hole, even when every issue is collected (errors: "all").
• The git overview sheet treats a blank deep-link ID as missing and closes, like the device preview screen. Its inspector copy already renders only behind the thread screen's blank-param guard.

Verification

• vp test run in packages/contracts: 37 files, 612 tests passed (web composerContextRecords.test.ts: 30). The new tests cover what follows, and each fails on main except the back-compat one, which pins existing behaviour:
  • a message context with one unencodable record encodes over the JSON codec and decodes to the other record;
  • a bare array drops the bad element on the wire;
  • an Array(Unknown)-wrapped array drops it too;
  • Schema.is rejects [undefined];
  • a context sends without the records the wire cannot carry: a non-JSON payload, a payload JSON.stringify throws on (a bigint), and an explicit undefined optional field;
  • a hole is a schema issue, not a thrown TypeError, under errors: "all";
  • null holes from servers on fix(contracts): trimmed IDs round-trip #16300 still decode.
• toJsonSchemaDocument output is byte-identical to main for every exported contracts schema, except the composer context records. Their optional fields no longer list null as an alternative, because they are optionalKey now. Nothing serves these documents (no MCP tool or OpenAPI route takes context records).
• vp exec tsc --noEmit -p . in packages/contracts, apps/server, apps/web and apps/mobile: all exit 0.
• vp lint on the changed files: clean.

Model/harness: Claude Opus 5.5 (1M context) via Claude Code in T3 Code.

🤖 Generated with Claude Code

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[macroscopeapp]

Approvability

Verdict: Approved at ef743e0

Macroscope's review found this PR approvable — The PR contains focused fixes for malformed context serialization and blank mobile deep links, with regression coverage for wrapped arrays, JSON-invalid payloads, and compatibility holes. Valid records and normal navigation paths remain unchanged, and no product defaults or static-analysis settings are modified.

^{You can add or adjust custom eligibility rules. Learn more.}

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 8ddf200 · PR result: ef743e0 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

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📝 Walkthrough

Walkthrough

The Git overview sheet validates route IDs before rendering. Forward-compatible arrays filter undefined values during encoding and reject them during validation. Composer context records apply stricter optional-field and JSON payload validation.

Changes

Git overview route IDs

Layer / File(s)	Summary
Validate route IDs before rendering apps/mobile/src/features/threads/git/GitOverviewSheet.tsx	The sheet navigates back and renders nothing when either route ID is blank. For nonblank IDs, it renders the extracted content component.

Contract encoding

Layer / File(s)	Summary
Filter and validate array values packages/contracts/src/baseSchemas.ts, packages/contracts/src/baseSchemas.test.ts	Array encoding filters undefined values, and encoded arrays reject undefined elements. Tests cover omitted unencodable elements, wrapper arrays, incoming null entries, and undefined values.
Validate composer context payloads packages/contracts/src/composerContext.ts, packages/contracts/src/composerContext.test.ts, apps/web/src/lib/composerContextRecords.test.ts	Optional record fields reject explicit undefined values. Unknown context payloads must be JSON values and remain within the existing serialized-length limit. Tests cover omission of invalid records, decoding failure for an undefined record, and comparisons when htmlPreview or source differs.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 98a39

No actionable merge-blocking risk was found in the reviewed changes.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description gives detailed problem, change, and verification sections. It does not provide the required scope and approval information. Mentioning the follow-up to #16300 does not establish mainta…	Add a Scope and approval section. Link the triaged issue or discussion and include the maintainer’s explicit approval of the direction and scope. If no prior approval is needed, explain why this is a very small, focused fix for an obvious b…

✅ Passed checks (3 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main change: an unencodable context record no longer causes the send to fail.

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Explanation

The description gives detailed problem, change, and verification sections. It does not provide the required scope and approval information. Mentioning the follow-up to #16300 does not establish maintainer approval or explain why this change qualifies for an approval exemption.

Resolution

Add a Scope and approval section. Link the triaged issue or discussion and include the maintainer’s explicit approval of the direction and scope. If no prior approval is needed, explain why this is a very small, focused fix for an obvious bug.

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Inline comments:
Review comments at @packages/contracts/src/composerContext.ts:
- Around line 249-258: Update the wire-side serialization check in the
`ComposerContext` schema to allow serialization failures through so
`ForwardCompatibleArray` can drop unencodable records, then add an aggregate
size check immediately after `ForwardCompatibleArray` to enforce the character
limit on retained records. Keep the encode-direction filtering and existing
per-record validation unchanged.

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[juliusmarminge]

@macroscope-app please re-evaluate approvability. The sparse-array finding that blocked the verdict has been answered and resolved. A probe at 98a3984 showed Schema.is and make reject both new Array(1) and [a, , b] (see the reply in that thread). The size-bound thread is resolved too, and the only commits since then merge main.

[macroscopeapp]

Re-evaluated: not approved. The size bound is enforced, but the sparse-array concern remains: Array.prototype.every() skips holes, so new Array(1) and [a, , b] pass the current filter. The test only covers explicit [undefined].

[juliusmarminge]

@macroscope-app Sparse arrays were already rejected before this commit. Effect's array parser reads every index from 0 to length - 1, so a missing index reaches the element schema as undefined and fails there, before this filter runs. The new test below also passes against the previous filter. To make it explicit, ef743e0 changes the hole check to walk every index (no every), and adds a test showing that Schema.is and make reject a sparse array ([a] with length = 2) as well as [undefined]. Please re-evaluate.