fix: stop draining queue on /clear (remove SessionEnd shim) (#2136)

* fix: stop draining queue on /clear (and on every other SessionEnd)

The SessionEnd hook was wired to session-complete on Claude Code, Gemini
CLI, the transcripts processor, the OpenCode plugin, and OpenClaw. All of
those paths called POST /api/sessions/complete, which marked the session
completed and abandoned every still-pending observation in the queue.

So typing /clear (or logging out, or quitting) wiped in-flight work that
the worker was perfectly happy to keep processing on its own.

Removed the entire shim:
- Deleted SessionEnd hook block in plugin/hooks/hooks.json
- Deleted src/cli/handlers/session-complete.ts and its registry entry
- Deleted POST /api/sessions/complete route + Zod schema in SessionRoutes
- Removed call from transcripts processor handleSessionEnd
- Removed call from opencode-plugin session.deleted handler
- Removed Gemini SessionEnd → session-complete mapping
- Removed openclaw scheduleSessionComplete + completionDelayMs + timer state
- Updated tests + comments accordingly

Explicit user-initiated deletion (DELETE /api/sessions/:id and
POST /api/sessions/:sessionDbId/complete from the viewer UI) still works
via SessionCompletionHandler.completeByDbId — that's the only path that
should drain the queue.

The worker self-completes via its SDK-agent generator's finally-block, so
no external completion call is needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: clarify opencode-plugin session.deleted is in-memory cleanup only

Greptile P2: file-level header still implied session.deleted called the
worker. Now it only cleans up the local contentSessionIdsByOpenCodeSessionId
map; worker self-completes via the SDK-agent generator finally-block.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/cli/adapters/gemini-cli.ts

@@ -5,11 +5,10 @@ import { AdapterRejectedInput, isValidCwd } from './errors.js';
  * Gemini CLI Platform Adapter
  *
  * Normalizes Gemini CLI's hook JSON to NormalizedHookInput.
- * Gemini CLI supports 11 lifecycle hooks; we register 8:
+ * Gemini CLI supports 11 lifecycle hooks; we register 7:
  *
  * Lifecycle:
  *   SessionStart  → context     (inject memory context)
- *   SessionEnd    → session-complete
  *   PreCompress   → summarize
  *   Notification  → observation (system events like ToolPermission)
  *
@@ -28,7 +27,7 @@ import { AdapterRejectedInput, isValidCwd } from './errors.js';
  * Base fields (all events): session_id, transcript_path, cwd, hook_event_name, timestamp
  *
  * Output format: { continue, stopReason, suppressOutput, systemMessage, decision, reason, hookSpecificOutput }
- * Advisory hooks (SessionStart, SessionEnd, PreCompress, Notification) ignore flow-control fields.
+ * Advisory hooks (SessionStart, PreCompress, Notification) ignore flow-control fields.
  */
 export const geminiCliAdapter: PlatformAdapter = {
   normalizeInput(raw) {