feat(telegram): ADR-0020 slice 1a TurnGate + mid-run steer

[chinkan]

Summary

ADR-0020 slice 1a: mid-run message queue for Telegram user turns.

• TurnGate per session_key(bot_id, user_id): at most one active turn; FIFO pending cap 10; full → QUEUE_FULL text (never silent drop).
• Telegram ingress: submit → on Start spawn a loop that runs run_telegram_user_turn then finish → Next::User / StepLimit / Idle | Scheduled; on Accepted react 👀; on Full reply with the queue-full sentence.
• Steer drains A/B in loop_runner via SteerFn / with_steer; queued text injected with a [Steer] prefix.
• /stop: cancel processing and turn_gate.clear (report how many queued messages were cleared).
• Removed dead ConversationManager::apply_steer and pending_injections path; lib.rs exports turn_gate.
• Injector harness waits for gate idle after chat drives (spawn is intentional so the dispatcher stays free).

Out of scope (later slices)

• 1b — schedule-through-gate coordination
• 1c — voice / media on the queue path
• 2 — portal 202 / generation identity alignment

Note / deviation

cancel_token_registry is kept: the gate serializes turns per key, so there is still one cancel token per key.

Refs: ADR-0020

Test plan / QA matrix

• Unit: turn_gate module tests + tests/mid_run_steer.rs
• cargo fmt --check
• cargo clippy --locked --all-targets -- -D warnings
• env -u RUSTFOX_GOOGLE_OAUTH_CLIENT_ID cargo test --locked (942 passed / 0 failed)
• Manual Telegram:
  • Mid-run second message gets 👀 and steers the active turn
  • Queue-full text when 10 are already waiting
  • /stop cancels and clears the queue
  • Step-limit sentence once, then clear / continue behavior as ADR-0020 Q6

[chinkan]

TL ACCEPT — ADR-0020 slice 1a @ 301568c

Reviewed tip 301568c (base 4f293f6) against ADR-0020 slice 1a only. Product GO already on record.

Passes

• TurnGate per session_key(bot_id, user_id): FIFO cap 10; QUEUE_FULL English refusal (not silent drop); text reply path is not gated by fully_silent.
• Telegram: submit → spawn turn (dispatcher free); Accepted → setMessageReaction(👀) only; reaction failure → warn!, no ack bubble.
• Steer drains A/B in AgenticLoop via with_steer; injection prefixed [Steer]; scheduled / /mode queue do not attach steer (pending left for finish).
• /stop: cancel_processing + turn_gate.clear with N; does not discard waiting scheduled tickets.
• Max-iterations: auto-continue once; second hit → locked step_limit_text(N); idle with queue kept.
• Dead pending_injections / apply_steer removed; cancel_token_registry kept (PO-ok).
• Unit turn_gate + tests/mid_run_steer.rs; CI Test green (~942); fmt/clippy green.

Out of scope (correctly left out)

• 1b schedule-through-gate (begin_scheduled not wired; parallel schedule+user still possible).
• 1c voice/media queue path; slice 2 portal.

Non-blocking follow-up (do not block 1a merge)

• Spawn-loop restore_pending(rest) under /mode queue can start leftovers as one-message-per-turn instead of one combined turn (ADR Decision 5). Default Steer path is fine; please fix when touching the spawn loop / before leaning on queue mode in QA.

No merge/tag from TL. Same-account standing → this is the ACCEPT record (issue comment), not the Approve button.

[chinkan]

TL ACCEPT — tip c2e7353 (re-ACCEPT after CodeQL #26 fix)

Delta from 301568c: tests/telegram_update_injector.rs wait_turn_idle panic no longer interpolates session_key (panic!("turn gate still active after 5s")). Matches PO/QA ask — no dismiss needed.

Prior TL ACCEPT on slice 1a still stands for the rest of the PR. Merge when QA GO (CI green on this tip + manual Telegram) lands. No tag.