fix(check): read the session_log payload, not the file

A traceability probe falsified this gate four hours after I shipped it. The
check was `grep -q 'session_id' "$dir/SKILL.md"` — file-scoped. So the probe
stripped session_id from all three documented payloads in tdd/SKILL.md, added
one prose line saying "the tool has a required session_id field", and the gate
returned 0. The exact regression it exists to prevent was back in the file, and
the gate said nothing.

The duration_ms rule was no better: it matched one spelling, the historical one.
Both of these passed — `"duration_ms": <wall-clock>` with a JSON-quoted key, and
`duration_ms: elapsed wall-clock ms` with no angle brackets. It was a regression
test against the nine strings that existed that morning, described in the commit
message as a rule.

Now each documented payload is checked on its own line and reported with a line
number, and duration_ms is rejected in any spelling unless it carries an actual
number — the objection was always to a placeholder no agent can fill, not to the
field.

Five new cases, each one a probe from that run: prose mentioning the word while
the payload omits it, one bad payload among several, both duration_ms spellings,
and a real measurement being allowed.

Also fixed while writing them: my first regex had `[[:space:]]*` before a
negated class that did not exclude whitespace, so the star matched empty and the
space itself tripped the check — a real measurement failed. The tests caught it
immediately, which is the argument for writing them from the probes rather than
from the intent.

Refs #36, #39
Bump-Type: patch

tests/check_session_log_test.sh

@@ -63,5 +63,38 @@ expect 1 'documenting duration_ms as wall-clock fails' \
   "$(fixture clock 'Call `session_log` with `{session_id: "<id>", skill: "alpha", duration_ms: <wall-clock>}`')" \
   'duration_ms'
 
+# --- the gate must read the PAYLOAD, not the file ---------------------------
+# A traceability probe falsified the original: it grepped the whole file for the
+# string "session_id", so stripping the field from every documented payload and
+# leaving the word once in prose passed cleanly. The exact regression the gate
+# exists to prevent was back in the file and the gate said nothing.
+
+expect 1 'a payload without session_id fails even when prose mentions the word' \
+  "$(fixture prose 'The tool has a required session_id field.
+
+Call `session_log` with `{skill: "alpha", phase: "red", final_status: "pass"}`')" \
+  'session_id'
+
+expect 1 'one bad payload among several fails' \
+  "$(fixture mixed 'Call `session_log` with `{session_id: "<id>", skill: "alpha", phase: "red"}`
+
+Then `session_log` with `{skill: "alpha", phase: "green", final_status: "pass"}`')" \
+  'session_id'
+
+# duration_ms was banned by matching exactly one spelling of it — the historical
+# one. Both of these passed the original gate.
+expect 1 'duration_ms with a JSON-quoted key fails' \
+  "$(fixture jsonkey 'Call `session_log` with `{session_id: "<id>", "duration_ms": <wall-clock>}`')" \
+  'duration_ms'
+
+expect 1 'duration_ms described in prose rather than angle brackets fails' \
+  "$(fixture prosems 'Call `session_log` with `{session_id: "<id>", duration_ms: elapsed wall-clock ms}`')" \
+  'duration_ms'
+
+# A real measurement is allowed: the objection is to a placeholder no agent can
+# fill, not to the field.
+expect 0 'a duration_ms carrying a real value is allowed' \
+  "$(fixture realms 'Call `session_log` with `{session_id: "<id>", duration_ms: 1430}`')"
+
 printf '\ncheck_session_log: %d passed, %d failed\n' "$pass" "$fail"
 [ "$fail" -eq 0 ]