#15732: [AI-assisted] feat: emit agent:response internal hook after replies

## Summary Adds an `agent:response` event on the internal hook bus, emitted after each completed reply dispatch. This enables internal consumers (bundled hooks, future features) to react to agent responses with session context stats. ### What changed - **New `agent:response` internal hook event** in `dispatch-from-config.ts` — fires after `dispatcher.waitForIdle()` with reply content, channel info, and session stats (context tokens, model, compaction count, etc.) - **Fixed session store resolution** — uses `cfg.session.store` and resolved `agentId` instead of defaults (was broken for multi-agent / custom store configs) - **Fixed session store key lookup** — adds lowercase fallback matching the existing pattern in `resolveSessionTtsAuto()` ### Context While building a Discord presence feature that shows live context usage, I discovered: 1. `message_sent` plugin hook already exists in `deliverOutboundPayloads()` with proper delivery status tracking 2. There was no post-reply internal hook for accessing session stats — this PR adds that The presence feature itself will be a separate PR pending design discussion. ### AI Disclosure - [x] This PR was developed with AI assistance (Claude via OpenClaw) - [x] All changes reviewed and tested by a human contributor - [x] No AI-generated test fixtures or snapshots ### Testing - All 12 existing tests in `dispatch-from-config.test.ts` pass - Build, lint, and format checks pass - Manually verified `agent:response` hook fires with correct session stats <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds a new internal hook emission (`agent:response`) from `dispatchReplyFromConfig` after replies have been dispatched and the dispatcher has gone idle. The event includes aggregated reply text, a channel/to identifier, and (when available) session stats loaded from the configured session store (including multi-agent store resolution and a lowercase session-key fallback). Tests were updated to include a `runMessageSent` mock reset, but the hook behavior itself is not directly exercised in the unit tests in this PR. <h3>Confidence Score: 3/5</h3> - This PR is likely safe to merge once the internal hook semantics are aligned with existing dispatch behavior. - Core changes are localized and largely additive, but the new `agent:response` event currently (1) omits fast-abort replies and (2) can report a channel value that doesn’t consistently reflect the dispatch/routing channel, which will break internal consumers relying on accurate attribution. - src/auto-reply/reply/dispatch-from-config.ts _{Last reviewed commit: 6afed29} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->