worker: make coder review routing durable

docs/report/2026-08-06-subworker-completion-idle-auto-run.md

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+# SubWorker completion notification did not wake an idle parent
+
+Date: 2026-08-06
+Ticket: `00001KZKNWP5X`
+
+## Observed behavior
+
+A Reviewer SubWorker finished after its parent Worker had returned to idle. Although the completion notification was marked `auto_run: true`, the parent did not run until the user submitted another message. The notification appeared only in that later turn.
+
+## Root cause
+
+The completion callback called `NotifyBuffer::push_notify(..., true)` directly. A running parent checks that buffer at turn end and can stage a follow-up, but an idle controller waits on its method channel. Writing the buffer alone therefore could not wake an already-idle parent.
+
+## Fix
+
+Normal controller-owned Workers now give the SubWorker tool a weak sender for the parent method channel. Completion is delivered through the existing:
+
+```rust
+Method::Notify {
+    message,
+    auto_run: true,
+}
+```
+
+path, which commits the notification through the normal inbox and wakes an idle controller. A `WeakSender` avoids a controller/tool/channel reference cycle that would otherwise keep the controller alive after external handles are dropped. Internal Worker sessions without a controller retain the direct buffer target.
+
+## Regression coverage
+
+- SubWorker completion sends exactly one `Method::Notify { auto_run: true }` to the parent controller channel.
+- The controller notification target does not keep the method channel alive after the strong sender is dropped.
+- Existing running-parent notification follow-up tests remain green.
+- `cargo test -p worker --lib`: 514 passed.