refactor: remove Pylon pair mode and thread delegation

.agents/durable-facts.jsonl

@@ -20,3 +20,4 @@
 {"id": "2026-09-16-agent-delegation-toolkit", "recorded_at": "2026-09-16T22:43:16Z", "scope": "server/mcp-delegation", "fact": "Agent delegation is a sidecar MCP toolkit (delegate_thread, delegated_thread_status, delegated_thread_result, send_to_delegated_thread, interrupt_delegated_thread) over existing orchestration commands and projections, with no events, decider branches, projectors, or migrations. A child thread's id is delegated:<parentThreadId>:<first 16 hex of sha256(parent + newline + key)>; ownership, one-level depth, and the eight-live-children limit all derive from that id. The delegation capability is minted only when enableAgentDelegation is on and never for a delegated: thread. Creates, meta updates, and turn starts use deterministic command ids; deletes and interrupts use a unique id per call. Waits are capped at 45 seconds because Prime Agent's MCP client cancels tool calls at 60 seconds. Only a starting session counts as pending admission, and a child is discarded as a crash orphan only with no initial message, session, turn, or rollback.", "source_commits": ["c09309c94fac140d05d0f74c0fce88aa27d9cabf"], "source_paths": ["apps/server/src/mcp/toolkits/delegation/logic.ts", "apps/server/src/mcp/toolkits/delegation/handlers.ts", "apps/server/src/mcp/toolkits/delegation/tools.ts", "apps/server/src/provider/Layers/ProviderService.ts", "docs/internals/delegation.md", "docs/user/agent-delegation.md"], "supersedes": []}
 {"id":"2026-09-17-agent-delegation-defaults","recorded_at":"2026-09-17T05:19:42Z","scope":"server/mcp-delegation","fact":"Delegation defaults are project-scoped settings: delegationDefaultModelSelection (null by default) and delegationChildRuntimeMode (inherit or approval-required). An agent-named provider always wins and ignores the default; with no provider, the default supplies the provider, plus its model and options unless the agent named a model, in which case the default options are dropped. With neither, delegate_thread fails with DelegationDefaultMissingError instead of guessing, and an unavailable default provider is an error, never a fallback. The child mode default applies only when the agent passes no runtimeMode, and every mode still resolves to the parent mode or approval-required, never broader. Model selections are whole values: the server patch and the web project-scope write both replace them instead of deep-merging, so a stale options object cannot survive a model change. Harnesses whose session holds the delegation capability get a <pylon_delegation> block in their runtime instructions; Prime Agent receives no Pylon runtime instructions and relies on the delegate_thread tool description for the same guidance.","source_commits":["3cfc8c3fbd0e4e4db10e7c6d2e79db86e0f0e748"],"source_paths":["packages/contracts/src/settings.ts","packages/shared/src/serverSettings.ts","apps/server/src/mcp/toolkits/delegation/logic.ts","apps/server/src/mcp/toolkits/delegation/handlers.ts","apps/server/src/mcp/toolkits/delegation/tools.ts","apps/server/src/provider/RuntimeInstructions.ts","apps/web/src/components/settings/scopedSettings.ts","apps/web/src/components/settings/ProjectDefaultsSettings.tsx","docs/internals/delegation.md","docs/user/agent-delegation.md"],"supersedes":[]}
 {"id":"2026-09-18-delegation-follow-through-observation","recorded_at":"2026-09-18T05:16:26Z","scope":"server/mcp-delegation","fact":"Automatic delegation follow-through is not a pure sidecar: it adds the internal thread.delegation.follow-through command, a decider admission branch, and two projection queries, so removing delegation means removing those with the toolkit and reactor. The reactor's observeDelegatedChild must agree with the toolkit's deriveDelegatedThreadState for completed children: a completed turn is observed as completed even when the session was stopped afterwards by a restart or the idle reaper, and only a non-terminal turn on a stopped session reads as interrupted. At startup every child whose observation key differs from the persisted one is baselined, never delivered.","source_commits":["6b71f09db74029e5d6d12dceb0b1997bae35394e"],"source_paths":["apps/server/src/orchestration/delegationFollowThrough.logic.ts","apps/server/src/orchestration/DelegationFollowThroughReactor.ts","docs/internals/delegation.md"],"supersedes":["2026-09-16-agent-delegation-toolkit"]}
+{"id":"2026-09-19-pylon-pair-delegation-removed","recorded_at":"2026-09-19T19:23:58.045941Z","scope":"server/mcp-delegation","fact":"Pylon pair mode and cross-provider thread delegation are removed. No pair/delegation MCP tools, shipped delegation skill, runtime routing protocol, follow-through command/reactor, executor lifecycle, settings, or native-subagent restrictions remain. Use provider-native subagents according to the user's instructions. Existing executor/child threads and history remain ordinary threads; no cleanup deletes them. New threads avoid pair-era provider context and per-session settings. Browser, device, computer, pull-request tools, opaque mobile draft IDs, whole-value model settings replacement, and shared-workspace rewind protection are preserved.","source_commits":["aca701395284523cfee09c3061cd0f1a463970a2"],"source_paths":["apps/server/src/mcp/McpHttpServer.ts","apps/server/src/provider/RuntimeInstructions.ts","apps/server/src/provider/Layers/ProviderService.ts","docs/user/updating.md"],"supersedes":["2026-09-16-agent-delegation-toolkit","2026-09-17-agent-delegation-defaults","2026-09-18-delegation-follow-through-observation"]}

apps/mobile/src/features/home/HomeRouteScreen.tsx

@@ -5,7 +5,6 @@ import { useEffect, useMemo, useState } from "react";
 import { Platform, useWindowDimensions } from "react-native";
 
 import { NativeHeaderToolbar, NativeStackScreenOptions } from "../../native/StackHeader";
-import { withoutPairExecutors } from "@t3tools/client-runtime/state/pair";
 import { useProjects, useThreadShells } from "../../state/entities";
 import { usePendingNewTasks } from "../../state/use-pending-new-tasks";
 import { useWorkspaceState } from "../../state/workspace";
@@ -30,8 +29,7 @@ export function HomeRouteScreen() {
   const { width: windowWidth } = useWindowDimensions();
   const { layout } = useAdaptiveWorkspaceLayout();
   const projects = useProjects();
-  const threadShells = useThreadShells();
-  const threads = useMemo(() => withoutPairExecutors(threadShells), [threadShells]);
+  const threads = useThreadShells();
   const { environments: workspaceEnvironments, state: catalogState } = useWorkspaceState();
   const { savedConnectionsById } = useSavedRemoteConnections();
   const navigation = useNavigation();

apps/mobile/src/features/threads/ThreadComposer.tsx

@@ -168,13 +168,10 @@ import {
 } from "../voice-input/ComposerDictationControl";
 import { useVoiceInputController } from "../voice-input/useVoiceInputController";
 import { resolveVoiceComposerPresentation } from "../voice-input/voiceInputPresentation";
-import { pairSettingsRow, type PairLead } from "@t3tools/client-runtime/state/pair-control";
-import { delegatedParentThreadId } from "@t3tools/shared/delegatedThreads";
 import {
   type ExistingThreadSettingsRouteSession,
   useExistingThreadSettingsRoutePresentation,
 } from "./ThreadSettingsSheet";
-import { usePairToggle } from "./usePairToggle";
 import {
   useThreadSettingsSheetPresentation,
   type NavigationWithFinishTransitioning,
@@ -1565,53 +1562,6 @@ export const ThreadComposer = memo(function ThreadComposer(props: ThreadComposer
       }),
     [currentModelOption?.capabilities, currentModelSelection.options],
   );
-  const isDelegatedThread = delegatedParentThreadId(props.selectedThread.id) !== null;
-  const lead = useMemo<PairLead>(
-    () => ({
-      id: props.selectedThread.id,
-      projectId: props.selectedThread.projectId,
-      title: props.selectedThread.title,
-      runtimeMode: props.selectedThread.runtimeMode,
-      branch: props.selectedThread.branch,
-      worktreePath: props.selectedThread.worktreePath,
-      session: props.selectedThread.session,
-    }),
-    [props.selectedThread],
-  );
-  const leadDriverKind = composerAuthority.provider?.driver ?? null;
-  const {
-    state: pairState,
-    executorSelection,
-    lockedReason: pairLockedReasonValue,
-    onToggle: onTogglePair,
-  } = usePairToggle({
-    environmentId: props.environmentId,
-    projectId: props.selectedThread.projectId,
-    lead,
-    leadDriverKind,
-  });
-  const executorLabel = executorSelection?.model ?? "";
-  const pairRow = useMemo(
-    () =>
-      pairSettingsRow({
-        state: pairState,
-        lockedReason: pairLockedReasonValue,
-        executorSelection,
-        executorLabel,
-      }),
-    [executorLabel, executorSelection, pairLockedReasonValue, pairState],
-  );
-  const pairSession = useMemo(
-    () =>
-      isDelegatedThread
-        ? undefined
-        : {
-            ...pairRow,
-            onToggle: onTogglePair,
-          },
-    [isDelegatedThread, onTogglePair, pairRow],
-  );
-
   const settingsOwnerId = composerOwnerKey;
   const settingsRouteSession = useMemo<ExistingThreadSettingsRouteSession>(
     () => ({
@@ -1633,14 +1583,12 @@ export const ThreadComposer = memo(function ThreadComposer(props: ThreadComposer
         if (!props.sessionInputBlocked) props.onUpdateRuntimeMode(mode);
       },
       getModelDisabledReason: getModelChangeDisabledReason,
-      ...(pairSession ? { pair: pairSession } : {}),
     }),
     [
       confirmSessionHarnessRefinement,
       currentModelSelection,
       currentRuntimeMode,
       getModelChangeDisabledReason,
-      pairSession,
       props.onUpdateModelSelection,
       props.onUpdateRuntimeMode,
       props.sessionInputBlocked,