fix(postmortem): anchor terminal_status on the structured Status line

The subagent terminal-status classifier scanned the whole final report
text for status keywords, so `\bBLOCKED\b` fired on the implement
end-report's own template lines (`BLOCKED file:  BLOCKED.md`,
`Blocked detail:`) and on prose narrating a surmounted blocker. Shipped
implement runs whose end-report reads `Status: DONE` were flipped to
BLOCKED — making the agent-effectiveness axis actively misleading.

Anchor on the structured `Status:` line of the end-report instead (the
implement-orchestrator emits a fixed `Status:  DONE|PARTIAL|BLOCKED|...`
header, optionally markdown-bold). Fall back to a status token standing
alone on its own line for agents that emit a bare terminal token; prose
mentions and `BLOCKED.md`-style substrings no longer match. Agents with
no structured status now read `unknown` rather than a fabricated BLOCKED.

Add an executable spec (postmortem/tests/test_terminal_status.py, plain
asserts, no pytest dep) pinning the issue-#3 case plus the genuine
BLOCKED / bare-token / no-signal guards. RED before, GREEN after.

Verified on the real AILang-style session 2811d227: 3 BLOCKED (one a
false positive) -> 2 genuine BLOCKED + 13 honest unknown.

closes #3

postmortem/tests/test_terminal_status.py

@@ -0,0 +1,125 @@
+#!/usr/bin/env python3
+"""Executable spec for postmortem.subagent_terminal_status.
+
+Run directly: `python3 postmortem/tests/test_terminal_status.py`.
+Exits 0 on pass, 1 on failure. No pytest dependency — the plugin has
+no test harness, and a status-classifier is small enough to pin with
+plain asserts.
+
+Pins issue #3: the terminal-status text-scan over-reports BLOCKED for
+shipped implement runs, because `\\bBLOCKED\\b` fires on the end-report's
+own template lines (`BLOCKED file:     BLOCKED.md`, `Blocked detail:`)
+and on prose narrating a surmounted blocker. The authoritative signal is
+the structured `Status:` line of the end-report, not any keyword
+occurrence in the body.
+"""
+
+import importlib.util
+import json
+import os
+import sys
+import tempfile
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+SCRIPT = os.path.join(HERE, "..", "scripts", "postmortem.py")
+
+spec = importlib.util.spec_from_file_location("postmortem", SCRIPT)
+pm = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(pm)
+
+
+def write_subagent_log(final_text):
+    """Write a one-assistant-turn subagent jsonl whose last text block is
+    `final_text`, return its path. Caller cleans up."""
+    fd, path = tempfile.mkstemp(suffix=".jsonl")
+    rec = {"type": "assistant",
+           "message": {"role": "assistant",
+                       "content": [{"type": "text", "text": final_text}]}}
+    with os.fdopen(fd, "w") as fh:
+        fh.write(json.dumps(rec) + "\n")
+    return path
+
+
+def status_of(final_text):
+    path = write_subagent_log(final_text)
+    try:
+        return pm.subagent_terminal_status(path)
+    finally:
+        os.unlink(path)
+
+
+# A realistic implement-orchestrator end-report that SHIPPED (Status: DONE)
+# but whose body carries the template's BLOCKED-bearing lines. This is the
+# exact shape that issue #3 reports as misclassified.
+SHIPPED_DONE_REPORT = """\
+Status:           DONE
+Iter:             0126-leg3
+Started from:     a1b2c3d
+Tasks completed:  3 of 3
+                  - poly RawBuf elem-var mono fix
+                  - series kernel module
+                  - owned-param tail-recursion leak
+Working tree:     dirty (7 files changed)
+BLOCKED file:     BLOCKED.md (uncommitted; only on PARTIAL/BLOCKED)
+Stats:            .claude/stats/0126.json (uncommitted)
+Files touched:    7
+Tests:            12 green, 0 red
+E2E coverage:     none (mini mode)
+Blocked detail:   (only if BLOCKED or PARTIAL — also written to BLOCKED.md)
+
+Note: task 2 hit a blocker early (missing fixture) which was resolved
+in-phase; no BLOCKED.md was written.
+"""
+
+GENUINE_BLOCKED_REPORT = """\
+Status:           BLOCKED
+Iter:             0127
+Started from:     d4e5f6a
+Tasks completed:  1 of 3
+Working tree:     dirty (2 files changed)
+BLOCKED file:     BLOCKED.md (uncommitted)
+Blocked detail:   Task: 2
+                  Reason: review-loop-exhausted
+                  Worker says: spec-compliance never reached approved
+"""
+
+PARTIAL_REPORT = """\
+Status:           PARTIAL
+Iter:             0128
+Tasks completed:  2 of 3
+BLOCKED file:     BLOCKED.md (uncommitted)
+"""
+
+CASES = [
+    # (name, final_text, expected)
+    ("shipped DONE with BLOCKED template lines (issue #3)",
+     SHIPPED_DONE_REPORT, "DONE"),
+    ("genuine BLOCKED end-report",
+     GENUINE_BLOCKED_REPORT, "BLOCKED"),
+    ("PARTIAL end-report mentioning BLOCKED.md",
+     PARTIAL_REPORT, "PARTIAL"),
+    ("narrating agent whose final line is a bare status token",
+     "Work complete, tests green.\n\nDONE", "DONE"),
+    ("prose mentioning a resolved blocker, no status line",
+     "I was briefly BLOCKED by a missing import but fixed it. All good.",
+     "unknown"),
+]
+
+
+def main():
+    failures = []
+    for name, text, expected in CASES:
+        got = status_of(text)
+        ok = got == expected
+        print(f"[{'PASS' if ok else 'FAIL'}] {name}: expected {expected!r}, got {got!r}")
+        if not ok:
+            failures.append(name)
+    if failures:
+        print(f"\n{len(failures)} failure(s).")
+        return 1
+    print(f"\nAll {len(CASES)} cases passed.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())