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/config/schema.help.ts

@@ -345,6 +345,10 @@ export const FIELD_HELP: Record<string, string> = {
     'DM session scoping: "main" keeps continuity; "per-peer", "per-channel-peer", or "per-account-channel-peer" isolates DM history (recommended for shared inboxes/multi-account).',
   "session.identityLinks":
     "Map canonical identities to provider-prefixed peer IDs for DM session linking (example: telegram:123456).",
+  "session.threadBindings.enabled":
+    "Global master switch for thread-bound session routing features. Channel/provider keys (for example channels.discord.threadBindings.enabled) override this default. Default: true.",
+  "session.threadBindings.ttlHours":
+    "Default auto-unfocus TTL in hours for thread-bound sessions across providers/channels. Set 0 to disable (default: 24). Provider keys (for example channels.discord.threadBindings.ttlHours) override this.",
   "channels.telegram.configWrites":
     "Allow Telegram to write config in response to channel events/commands (default: true).",
   "channels.slack.configWrites":
@@ -439,6 +443,12 @@ export const FIELD_HELP: Record<string, string> = {
   "channels.discord.retry.maxDelayMs": "Maximum retry delay cap in ms for Discord outbound calls.",
   "channels.discord.retry.jitter": "Jitter factor (0-1) applied to Discord retry delays.",
   "channels.discord.maxLinesPerMessage": "Soft max line count per Discord message (default: 17).",
+  "channels.discord.threadBindings.enabled":
+    "Enable Discord thread binding features (/focus, bound-thread routing/delivery, and thread-bound subagent sessions). Overrides session.threadBindings.enabled when set.",
+  "channels.discord.threadBindings.ttlHours":
+    "Auto-unfocus TTL in hours for Discord thread-bound sessions (/focus and spawned thread sessions). Set 0 to disable (default: 24). Overrides session.threadBindings.ttlHours when set.",
+  "channels.discord.threadBindings.spawnSubagentSessions":
+    "Allow subagent spawns with thread=true to auto-create and bind Discord threads (default: false; opt-in). Set true to enable thread-bound subagent spawns for this account/channel.",
   "channels.discord.ui.components.accentColor":
     "Accent color for Discord component containers (hex). Set per account via channels.discord.accounts.<id>.ui.components.accentColor.",
   "channels.discord.voice.enabled":