MC-4500

Coder gate for MC-4494 / Control Room v2 second behavior-changing slice. Objective: Under the existing default-off `MC_CONTROL_ROOM_V2_CONTROLLER_NOTIFY` flag, make human ticket comments notify the Controller instead of auto-routing/reopening/requeueing/dispatching runtimes. This is the MC API comment route slice only. Preceding landed work: - MC-4496: inert role registry/audit schema landed. - MC-4499: WAT/workflow dispatch actions under the same flag now notify Controller instead of auto-dispatching. Target anchors from preflight: - app.py `api_add_comment()` - app.py `_route_human_comment()` - app.py `_queue_and_pickup()` should not be called by human comments under flag. - comment persistence through `models.add_comment()` must remain. Required behavior when flag is ON: - Human comment is persisted normally. - A durable Controller notification/audit comment or event is created, clearly saying Controller must decide next action. - API response clearly indicates Controller notification, e.g. `controller_notify: true` / `queued_for_controller: true`. - Do NOT call `_route_human_comment()` for ordinary human comments. - Do NOT call `_queue_and_pickup()`. - Do NOT auto-assign mentions like @luci/@larry/@tessa/@atlas in this slice. - Do NOT reopen terminal tickets, flip `in_review` to `todo`, resume/send to runtime, or create queued_messages from a human comment. - System/controller/internal explicit actions can remain outside this if needed; keep scope narrow and safe. Required behavior when flag is OFF: - Existing comment route behavior remains unchanged. Tests: - Flag-on human comment on in_review/in_progress/needs_input/done persists comment + controller notification and does not call route/pickup/status mutation. - Flag-on @mention does not auto-assign/auto-pickup. - Flag-off preserves existing routing path (mock/assert `_route_human_comment` is called where current behavior expects it). - Existing relevant tests remain green: comment/telegram bridge tests if cheap, workflow idempotency if affected. Constraints: - Do not change Telegram bridge direct send path in this slice; later slice. - Do not change board grouping/statuses in this slice. - Runtime/model guidance remains advisory and Controller-owned. - Use project hooks/dev-loop as required. Expected check-in: 2026-05-31 18:08:45 UTC.