fix(pm): keep the production spawn naming TOOL, so the gate keeps its RUN edge

The first draft routed both the real and the substituted child through one
`resolve(ROOT, child)` call. The tool's derivation follows that spawn as a RUN
edge to inherit TOOL's watch hints — the workflow tree among them — and its run
scan refuses a rebound program component, so the edge vanished: five cases of
the tool's own 1730-case battery red, and a workflows-only surface stopped
deriving `check:pm-dispatch-gates` at all (measured 1 -> 0 on
.github/workflows/board-snapshot.yml).

The substituted child now gets its own call and the production one is the
expression that was there before.

Claude-Session: https://claude.ai/code/session_01HZfg2AwVX191qCizp88gQr
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

scripts/pm/check-dispatch-gates.mjs

@@ -316,7 +316,23 @@ if (child !== TOOL) {
 }
 
 const started = Date.now();
-const result = spawnSync(process.execPath, [resolve(ROOT, child), '--self-test'], { stdio: 'inherit' });
+/**
+ * ⛔ The production spawn names TOOL DIRECTLY, and it has to keep doing so.
+ *
+ * The tool's derivation follows this call as a RUN edge, which is how this gate
+ * inherits TOOL's own watch hints — the workflow tree among them — so that a
+ * card touching only `.github/workflows` derives this gate at all. That scan
+ * refuses a REBOUND program component on purpose, so collapsing both spawns
+ * into one `resolve(ROOT, child)` silently cuts the edge. Measured when this
+ * file's self-test was first written that way: five cases of the tool's own
+ * battery red, and a workflows-only derivation stopped naming this gate
+ * entirely. The substituted child therefore gets its OWN call, and the
+ * production one is byte-for-byte the expression that was here before.
+ */
+const result =
+  childAt < 0
+    ? spawnSync(process.execPath, [join(ROOT, TOOL), '--self-test'], { stdio: 'inherit' })
+    : spawnSync(process.execPath, [resolve(ROOT, child), '--self-test'], { stdio: 'inherit' });
 /**
  * What the battery cost on THIS box, printed rather than frozen anywhere.
  *