feat: thread-bound subagents on Discord (#21805)

* docs: thread-bound subagents plan

* docs: add exact thread-bound subagent implementation touchpoints

* Docs: prioritize auto thread-bound subagent flow

* Docs: add ACP harness thread-binding extensions

* Discord: add thread-bound session routing and auto-bind spawn flow

* Subagents: add focus commands and ACP/session binding lifecycle hooks

* Tests: cover thread bindings, focus commands, and ACP unbind hooks

* Docs: add plugin-hook appendix for thread-bound subagents

* Plugins: add subagent lifecycle hook events

* Core: emit subagent lifecycle hooks and decouple Discord bindings

* Discord: handle subagent bind lifecycle via plugin hooks

* Subagents: unify completion finalizer and split registry modules

* Add subagent lifecycle events module

* Hooks: fix subagent ended context key

* Discord: share thread bindings across ESM and Jiti

* Subagents: add persistent sessions_spawn mode for thread-bound sessions

* Subagents: clarify thread intro and persistent completion copy

* test(subagents): stabilize sessions_spawn lifecycle cleanup assertions

* Discord: add thread-bound session TTL with auto-unfocus

* Subagents: fail session spawns when thread bind fails

* Subagents: cover thread session failure cleanup paths

* Session: add thread binding TTL config and /session ttl controls

* Tests: align discord reaction expectations

* Agent: persist sessionFile for keyed subagent sessions

* Discord: normalize imports after conflict resolution

* Sessions: centralize sessionFile resolve/persist helper

* Discord: harden thread-bound subagent session routing

* Rebase: resolve upstream/main conflicts

* Subagents: move thread binding into hooks and split bindings modules

* Docs: add channel-agnostic subagent routing hook plan

* Agents: decouple subagent routing from Discord

* Discord: refactor thread-bound subagent flows

* Subagents: prevent duplicate end hooks and orphaned failed sessions

* Refactor: split subagent command and provider phases

* Subagents: honor hook delivery target overrides

* Discord: add thread binding kill switches and refresh plan doc

* Discord: fix thread bind channel resolution

* Routing: centralize account id normalization

* Discord: clean up thread bindings on startup failures

* Discord: add startup cleanup regression tests

* Docs: add long-term thread-bound subagent architecture

* Docs: split session binding plan and dedupe thread-bound doc

* Subagents: add channel-agnostic session binding routing

* Subagents: stabilize announce completion routing tests

* Subagents: cover multi-bound completion routing

* Subagents: suppress lifecycle hooks on failed thread bind

* tests: fix discord provider mock typing regressions

* docs/protocol: sync slash command aliases and delete param models

* fix: add changelog entry for Discord thread-bound subagents (#21805) (thanks @onutc)

---------

Co-authored-by: Shadow <hi@shadowing.dev>

src/agents/subagent-registry-state.ts

@@ -0,0 +1,56 @@
+import {
+  loadSubagentRegistryFromDisk,
+  saveSubagentRegistryToDisk,
+} from "./subagent-registry.store.js";
+import type { SubagentRunRecord } from "./subagent-registry.types.js";
+
+export function persistSubagentRunsToDisk(runs: Map<string, SubagentRunRecord>) {
+  try {
+    saveSubagentRegistryToDisk(runs);
+  } catch {
+    // ignore persistence failures
+  }
+}
+
+export function restoreSubagentRunsFromDisk(params: {
+  runs: Map<string, SubagentRunRecord>;
+  mergeOnly?: boolean;
+}) {
+  const restored = loadSubagentRegistryFromDisk();
+  if (restored.size === 0) {
+    return 0;
+  }
+  let added = 0;
+  for (const [runId, entry] of restored.entries()) {
+    if (!runId || !entry) {
+      continue;
+    }
+    if (params.mergeOnly && params.runs.has(runId)) {
+      continue;
+    }
+    params.runs.set(runId, entry);
+    added += 1;
+  }
+  return added;
+}
+
+export function getSubagentRunsSnapshotForRead(
+  inMemoryRuns: Map<string, SubagentRunRecord>,
+): Map<string, SubagentRunRecord> {
+  const merged = new Map<string, SubagentRunRecord>();
+  const shouldReadDisk = !(process.env.VITEST || process.env.NODE_ENV === "test");
+  if (shouldReadDisk) {
+    try {
+      // Persisted state lets other worker processes observe active runs.
+      for (const [runId, entry] of loadSubagentRegistryFromDisk().entries()) {
+        merged.set(runId, entry);
+      }
+    } catch {
+      // Ignore disk read failures and fall back to local memory.
+    }
+  }
+  for (const [runId, entry] of inMemoryRuns.entries()) {
+    merged.set(runId, entry);
+  }
+  return merged;
+}