Factor `child_in_debug()` state sampling

`_try_cancel_then_kill()` repeated the same child/tree debugger
predicate before and after its cancel-RPC checkpoint. Inline
duplication obscured that lock state must be sampled at both points.

Factor the predicate into a local `child_in_debug()` sampler. Use it
for initial hard-kill protection and re-run it after the await before
debugger waiting, preserving dynamic lock-state behavior. Keep it
local since one input is supervisor-owned nursery configuration.

Review: PR #481 (goodboy)
https://github.com/goodboy/tractor/pull/481#pullrequestreview-5012942328

Prompt-IO: ai/prompt-io/opencode/20260824T225356Z_2f86dd1a_prompt_io.md

(this patch was generated in some part by `opencode` using `gpt-5.6-sol` (`openai`))

ai/prompt-io/opencode/20260824T225356Z_2f86dd1a_prompt_io.md

@@ -0,0 +1,39 @@
+---
+model: openai/gpt-5.6-sol
+service: opencode
+session: d9d7df2c-7044-463f-8768-ec024718eac9
+timestamp: 2026-08-24T22:53:56Z
+git_ref: 2f86dd1a
+scope: code
+substantive: true
+raw_file: 20260824T225356Z_2f86dd1a_prompt_io.raw.md
+---
+
+## Prompt
+
+Continue PR #481 review remediation after committing the paired
+`ActorNursery` reap-state invariant. The human selected "keep" for the
+reviewer's request to factor a duplicated debugger predicate in
+`_try_cancel_then_kill()`.
+
+## Response summary
+
+Factor the child/tree debugger predicate into a local sampler used both
+before and after the cancel-RPC checkpoint. Preserve dynamic debugger
+lock re-evaluation and its distinction from root-wide debug mode.
+
+## Files changed
+
+- `tractor/runtime/_supervise.py` - factor the duplicated debugger
+  predicate without changing cancellation behavior.
+
+## Human edits
+
+The human explicitly selected "keep" after receiving keep/defer/drop
+options for this isolated review item. During commit-plan review, the
+agent found that a single pre-checkpoint snapshot could become stale;
+the human selected a local helper which re-evaluates the lock after the
+cancel RPC. The human then considered moving the predicate into
+`.devx.debug` and accepted keeping it local after confirming that no
+existing helper shares its supervisor-owned semantics. No direct
+source-line edits were made by the human.

ai/prompt-io/opencode/20260824T225356Z_2f86dd1a_prompt_io.raw.md

@@ -0,0 +1,18 @@
+---
+model: openai/gpt-5.6-sol
+service: opencode
+timestamp: 2026-08-24T22:53:56Z
+git_ref: 2f86dd1a
+diff_cmd: git diff HEAD~1..HEAD
+---
+
+Implement the approved PR #481 review refactor in
+`_try_cancel_then_kill()` without changing debugger behavior.
+
+> `git diff HEAD~1..HEAD -- tractor/runtime/_supervise.py`
+
+Compute the child/tree debugger predicate once, reuse it in the broader
+hard-kill protection predicate, and pass it directly to
+`debug.maybe_wait_for_debugger()`.
+
+Run focused debugger/cancellation coverage and lint after the edit.

tractor/runtime/_supervise.py

@@ -130,12 +130,21 @@ async def _try_cancel_then_kill(
     # mutated by per-child `debug_mode=True`). ORing covers
     # every flavor without false-positively skipping
     # legitimate hard-kill paths in non-debug trees.
-    debug_protected: bool = (
+    def child_in_debug() -> bool:
+        '''
+        Sample child/tree debugger protection state.
+
+        '''
+        return (
+            debug_mode_active
+            or
             debug.Lock.ctx_in_debug is not None
+        )
+
+    debug_protected: bool = (
+        child_in_debug()
         or
         _state._runtime_vars.get('_debug_mode', False)
-        or
-        debug_mode_active
     )
 
     try:
@@ -145,11 +154,8 @@ async def _try_cancel_then_kill(
         if not cancelled:
             if debug_protected:
                 await debug.maybe_wait_for_debugger(
-                    child_in_debug=(
+                    # Re-sample after the cancel-RPC checkpoint.
-                        debug_mode_active
+                    child_in_debug=child_in_debug(),
-                        or
-                        debug.Lock.ctx_in_debug is not None
-                    ),
                     header_msg=(
                         'Delaying subproc hard-reap while '
                         'debugger locked..\n'