fix(telemetry): one-shot setup events never sweep other sessions' pending markers

gstack-telemetry-log finalizes every .pending-<session> marker that is not
the caller's own as outcome:unknown and deletes it. setup's onboarding
events (_setup_welcome, _setup_playwright) have no session of their own, so
a Chromium bootstrap failure during a live skill session recorded a false
unknown for that session and removed its marker.

New --no-sweep flag skips the stale-marker pass; both setup call sites use
it (the synthetic --session-id did not prevent the sweep). Surfaced by the
Codex adversarial pass.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

bin/gstack-telemetry-log

@@ -10,6 +10,11 @@
 #   gstack-telemetry-log --skill qa --duration 142 --outcome success \
 #     --used-browse true --session-id "12345-1710756600"
 #
+#   --no-sweep  one-shot events with no session of their own (setup's
+#               onboarding events) must not finalize OTHER sessions' in-flight
+#               .pending markers as outcome:unknown — only a skill's own
+#               epilogue may sweep.
+#
 # Env overrides (for testing):
 #   GSTACK_STATE_DIR  — override ~/.gstack state directory
 #   GSTACK_DIR        — override auto-detected gstack root
@@ -48,9 +53,11 @@ SEC_PAYLOAD_HASH=""
 SEC_CONFIDENCE=""
 SEC_LAYER=""
 SEC_VERDICT=""
+NO_SWEEP=""
 
 while [ $# -gt 0 ]; do
   case "$1" in
+    --no-sweep)      NO_SWEEP=1; shift ;;
     --skill)         SKILL="$2"; shift 2 ;;
     --duration)      DURATION="$2"; shift 2 ;;
     --outcome)       OUTCOME="$2"; shift 2 ;;
@@ -93,7 +100,10 @@ fi
 # ─── Finalize stale .pending markers ────────────────────────
 # Each session gets its own .pending-$SESSION_ID file to avoid races
 # between concurrent sessions. Finalize any that don't match our session.
+# --no-sweep (one-shot events from setup) skips this: a marker that is not
+# ours is another live session's, not a stale one.
 for PFILE in "$PENDING_DIR"/.pending-*; do
+  [ -z "$NO_SWEEP" ] || break
   [ -f "$PFILE" ] || continue
   # Skip our own session's marker (it's still in-flight)
   PFILE_BASE="$(basename "$PFILE")"