fix(claude): resolve queue-operation prompt completion deadlock

[nixecn]

Problem

When CCB delivers a prompt to Claude via tmux paste-buffer while the Claude
REPL is busy (cooking / tool_use), Claude CLI records it as

type=queue-operation, operation=enqueue, content=<prompt>

and does not synthesize a type=user message. The completion pipeline was
blind to queue-operation records: structured_event() dropped them entirely, so

• handle_user_event() never saw the CCB_REQ_ID anchor;
• anchor_seen stayed False;
• every subsequent assistant event (including the final end_turn, and the
  last_assistant_uuid needed for turn_duration matching) was gated out;
• the attempt hung in running forever, backing up the mailbox queue.

Field impact: repeated pm (central dispatcher) stalls, because pm is the
agent that most often receives async replies while busy. A 183-job sample
of the pm session log found 14 queue-op prompt deliveries; 9 of them
failed to complete automatically (7 incomplete, 2 cancelled by human recovery).

Full diagnosis: docs/claude-queue-operation-completion-deadlock-diagnosis.md
(added by this PR, 183 lines).

Fix

Three coordinated changes:

1. Synthesize a user event from queue-operation records
   (lib/provider_backends/claude/comm_runtime/parsing_runtime/structured.py)

   structured_event() now emits a role=user event for
   queue-operation/enqueue entries carrying the full prompt text, so the
   CCB_REQ_ID anchor is observed and anchor_seen flips.

2. Emit zero-text assistant events for tool_use / thinking-only entries
   (same file)

   Previously dropped because extract_message yielded no visible text.
   These carry the assistant uuid so pre-anchor bookkeeping can track
   last_assistant_uuid and the later turn_duration system event's
   parent_uuid matches.

3. Pre-anchor uuid bookkeeping
   (lib/provider_backends/claude/execution_runtime/polling.py)

   _process_event() now runs a bookkeeping pass on every assistant event
   (uuid tracking only) before the anchor_seen gate. Full
   chunk/reply/turn-boundary handling still requires anchor_seen.

Total: +335 / -2 across 3 files (docs + 2 code files).

Verification

• All 14 historical queue-op stuck jobs (sampled from the pm session)
  now reach TURN_BOUNDARY under the patched detector.
• The idle-REPL (user/text_string) path is unchanged — regression on
  normal prompts passes.
• Test suites:

  $ python3.11 -m pytest test/ -q -k "claude and (parsing or event_reading or exec_polling or assistant_events or queue_operation)"
  10 passed
  $ python3.11 -m pytest test/ -q -k "structured or polling"
  55 passed
  

[nixecn]

这个PR修改的内容，已经经过一段时间使用的验证了。 所以可以放心合并。