fix(#4217): reconcile artifacts before classifying an abnormally-ended executor (#4442)

* fix(#4217): reconcile artifacts before classifying abnormal ends

* test(#4217): pin the completion-reconciliation contract

* chore(#4217): regen derived inventory and install-tree fixtures

* test(#4217): follow the #4003 anchoring pins into the reconciliation fragment

Emitted-Drift-Ack-Growth: execute-phase.md — the runtime-neutral completion-reconciliation pointer, the two Codex wait-rule bindings, and the step-7 reconcile-first gate net +33 bytes over the extracted fallback block (#4217)

* chore(#4217): add changeset fragment

* chore(#4217): backfill PR number in changeset fragment

---------

Co-authored-by: sim <sim@local>

gsd-core/workflows/execute-phase/steps/completion-reconciliation.md

@@ -0,0 +1,53 @@
+# Completion reconciliation (#4217, split A of #3754)
+
+Read and follow this fragment from `execute-phase.md` step 4 whenever an executor's
+completion is in question. It owns the whole reconciliation policy — both arms — so the
+host wait step stays inside the ADR-857 Phase 6 byte ceiling (#1168).
+
+**Reconcile FIRST, classify SECOND.** How the child's session ended is bookkeeping
+about the transport; what it wrote to disk and to git is the evidence about the work.
+
+## When this runs
+
+1. **No terminal response** — a spawned agent does not return a normal terminal
+   completion signal but appears to have finished its work (or may still be running).
+2. **Abnormal end** — the child's session ended without a normal terminal completion
+   response: interrupted, aborted, closed, killed, timed out, or ended `turn_aborted` —
+   INCLUDING ends the orchestrator itself initiated. **An abnormally-ended child is
+   not evidence of failure (#4217):** the orchestrator's own interrupt/close says
+   nothing about whether the work completed; only the artifacts do.
+
+This policy applies to EVERY runtime and every isolation path — harness `Agent()`
+dispatches, orchestrator-worktree process spawns, and sequential dispatch alike. Never
+block indefinitely waiting for a signal; verify via filesystem and git state.
+
+## Probes (per plan in the wave)
+
+```bash
+# For each plan in this wave, check if the executor finished:
+SUMMARY_EXISTS=$(test -f "{phase_dir}/{plan_number}-{plan_padded}-SUMMARY.md" && echo "true" || echo "false")
+# #4003: anchored, zero-pad-tolerant scope (see safe_resume_gate); --since stays.
+SPOT_PHASE_N=$((10#{phase_number}))
+SPOT_PLAN_N=$((10#{plan_padded}))
+COMMITS_FOUND=$(git log --oneline --all -E --grep="^[a-z]+\((0*${SPOT_PHASE_N})-(0*${SPOT_PLAN_N})\):" --since="1 hour ago" | head -1)
+COMMITS_SINCE_DISPATCH=$(git log "${EXPECTED_BRANCH}" --since="${DISPATCH_TS}" --oneline | head -1)
+```
+
+## Verdicts
+
+**If SUMMARY.md exists AND matching commits are found:** the agent completed
+successfully — treat the plan as complete WITHOUT requiring another terminal child
+response, proceed to step 5, and do NOT re-dispatch a fresh executor for this plan:
+the work is already committed, and a second executor would redo it on top of itself.
+Log: `"✓ {Plan ID} completed (verified via spot-check — completion signal not received)"`.
+
+**If SUMMARY.md does NOT exist after a reasonable wait:** the agent may still be
+running or may have failed silently. Check `git log --oneline -5` for recent
+activity. If commits are still appearing, wait longer. If no activity, report the
+plan as failed and route to the failure handler in step 6.
+
+Evidence is BOTH probes or neither: a SUMMARY without matching commits, and matching
+commits without a SUMMARY, are each incomplete evidence — never auto-complete on one
+of them. When an abnormal end reconciles to no completion evidence, it stays failed:
+route to the failure handler exactly as a normal failure would, and let the
+safe-resume gate handle any un-summarized commits on the next run.