fix: address three Codex P2 review findings

1. Shebang (Codex P2): scripts/agent-bootstrap.sh and .claude/hooks/session-start.sh
   now use #!/usr/bin/env bash instead of #!/bin/bash, matching repo convention
   enforced by checkers.sh.

2. Fail-closed bd pin (Codex P2): .claude/hooks/session-start.sh local path now
   exits 2 with a warning when pinned or running version cannot be parsed,
   instead of silently succeeding. An unparseable version is not a pass.

3. pr-reviews failure (Codex P2): scripts/pr-watch no longer uses '|| true' to
   swallow pr-reviews failures. If pr-reviews fails (fetch error, malformed
   response), pr-watch now exits 6 with a warning. Empty successful fetch
   (no reviews) is still exit 0.

   - Added exit 6 to usage text and skill documentation
   - Added test case 'pr-reviews failure exits 6' using malformed JSON fixture
   - All 57 pr-watch tests pass

Co-authored-by: Ed Langley <fiddlerwoaroof@users.noreply.github.com>

.agents/skills/pr-watch/SKILL.md

@@ -16,8 +16,8 @@ scripts/pr-watch <pr-number> [--expect <sha>] [--timeout <sec>] [--interval <sec
 ```
 
 ```
-exit 0  every check COMPLETED, none failed, and MERGEABLE with a state of
-        CLEAN, UNSTABLE or HAS_HOOKS
+exit 0  every check COMPLETED, none failed, MERGEABLE with a state of
+        CLEAN, UNSTABLE or HAS_HOOKS, and reviews fetched (if --reviews)
 exit 1  a check failed (under any mergeability, BLOCKED included), or the
         PR is not mergeable (CONFLICTING, DIRTY, BEHIND, DRAFT, or a state
         it does not know)
@@ -27,6 +27,7 @@ exit 3  timed out with checks still running, mergeability still UNKNOWN,
 exit 4  usage or environment error
 exit 5  the PR is MERGED or CLOSED, at the head the watch pinned; it ends on
         the first poll that sees it closed, which may be mid-wait
+exit 6  checks green/mergeable, but pr-reviews failed (fetch error, not "no reviews")
 ```
 
 **`--reviews`** (default): after checks complete, print all reviews and comments

.claude/hooks/session-start.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Prepare a Claude Code on the web container for work on this repository.
 #
 # This hook delegates to the shared `scripts/agent-bootstrap.sh`, which works
@@ -33,7 +33,19 @@ if [ "${CLAUDE_CODE_REMOTE:-}" != "true" ]; then
   if command -v bd >/dev/null 2>&1; then
     pinned=$(beads_pin)
     running=$(bd_running_version)
-    if [ -n "$pinned" ] && [ -n "$running" ] && [ "$running" != "$pinned" ]; then
+    # Fail closed: if we can't parse either version, warn rather than silently pass
+    if [ -z "$pinned" ]; then
+      printf '[session-start] WARNING: cannot parse beads pin from flake.nix\n' >&2
+      printf '[session-start] The pin check is skipped, but mutating bd commands may be unsafe.\n' >&2
+      exit 2
+    fi
+    if [ -z "$running" ]; then
+      printf '[session-start] WARNING: cannot parse bd version from "bd version"\n' >&2
+      printf '[session-start] bd: %s\n' "$(command -v bd)" >&2
+      printf '[session-start] The pin check is skipped, but mutating bd commands may be unsafe.\n' >&2
+      exit 2
+    fi
+    if [ "$running" != "$pinned" ]; then
       printf '\n[session-start] ===== BEADS VERSION SKEW =====\n' >&2
       printf '[session-start] pinned (flake.nix): %s\n' "$pinned" >&2
       printf '[session-start] running:            %s  (%s)\n' "$running" "$(command -v bd)" >&2

scripts/agent-bootstrap.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Stack-agnostic agent bootstrap for this repository.
 #
 # This script prepares any coding agent (Claude Code, Cursor, etc.) to work

scripts/pr-watch

@@ -14,16 +14,16 @@ usage: pr-watch <pr-number> [--expect <sha>] [--timeout <sec>] [--interval <sec>
   --no-reviews      skip the reviews/comments printout
 
 exit 0  every check COMPLETED, none failed, and GitHub says MERGEABLE with a
-        state of CLEAN, UNSTABLE or HAS_HOOKS
+        state of CLEAN, UNSTABLE or HAS_HOOKS (and reviews fetched if --reviews)
 exit 1  a check failed, or the PR is not mergeable (any other known state)
 exit 2  the head moved during the wait, or is not --expect
 exit 3  timed out with checks still running, or mergeability still UNKNOWN,
         or still BLOCKED with every registered check green
 exit 4  usage or environment error
 exit 5  the PR is MERGED or CLOSED, so there is nothing left to wait for
+exit 6  checks green/mergeable, but pr-reviews failed (fetch error, not "no reviews")
 
-After exit 0, reviews and comments are printed (unless --no-reviews). These do
-not change the exit code -- answering them is your responsibility. Reviews are
+After exit 0, reviews and comments are printed (unless --no-reviews). Reviews are
 a separate API surface from comments; Codex/ChatGPT reviews arrive as *reviews*
 and are easy to miss if you only read the comment thread.
 EOF
@@ -146,21 +146,25 @@ case "$state" in CLEAN|UNSTABLE|HAS_HOOKS) ;; *) exit 1 ;; esac
 # ── Reviews and comments ───────────────────────────────────────────────────
 # Checks are green and mergeable. Show reviews/comments so the agent sees any
 # feedback that needs answering before merge. This does not change the exit
-# code -- answering reviews is your responsibility.
+# code for success -- answering reviews is your responsibility. However, if
+# pr-reviews itself fails (usage error, network, etc.), we warn and exit 6.
 if [ "$SHOW_REVIEWS" -eq 1 ]; then
   echo ""
   echo "pr-watch: fetching reviews and comments (--no-reviews to skip)…"
-  # pr-reviews' exit code is not propagated: reviews being present or absent
-  # does not change whether the PR is green/mergeable. The agent must read
-  # and answer them, but that is a human-in-the-loop obligation, not a gate.
-  # Fixture mode: pass through the fixture dir if set.
+  reviews_exit=0
   if [ -n "${PR_WATCH_FIXTURE_DIR:-}" ]; then
-    PR_REVIEWS_FIXTURE_DIR="$PR_WATCH_FIXTURE_DIR" "$SCRIPT_DIR/pr-reviews" "$PR" || true
+    PR_REVIEWS_FIXTURE_DIR="$PR_WATCH_FIXTURE_DIR" "$SCRIPT_DIR/pr-reviews" "$PR" || reviews_exit=$?
   else
-    "$SCRIPT_DIR/pr-reviews" "$PR" || true
+    "$SCRIPT_DIR/pr-reviews" "$PR" || reviews_exit=$?
   fi
   echo ""
+  if [ "$reviews_exit" -eq 0 ]; then
     echo "pr-watch: reviews shown above. Answer substantive feedback before merging."
+  else
+    echo "pr-watch: WARNING: pr-reviews failed (exit $reviews_exit). Reviews may not be shown." >&2
+    echo "pr-watch: Run './scripts/pr-reviews $PR' manually to fetch reviews." >&2
+    exit 6
+  fi
 fi
 
 exit 0

scripts/pr-watch-test.sh

@@ -99,6 +99,18 @@ else
   ok "--no-reviews actually skips review output"
 fi
 
+# pr-reviews failure: if pr-reviews fails, pr-watch exits 6 (not 0)
+# Create a green fixture with MALFORMED review fixtures so pr-reviews fails
+mk "$work/green-bad-reviews" last.json <<'EOF'
+{"headRefOid":"aaaaaaaaaaaa","mergeable":"MERGEABLE","mergeStateStatus":"CLEAN","statusCheckRollup":[
+ {"name":"build","status":"COMPLETED","conclusion":"SUCCESS"}]}
+EOF
+# Create malformed JSON that will cause jq to fail in pr-reviews
+echo 'NOT VALID JSON' > "$work/green-bad-reviews/last.pr.json"
+echo '[]' > "$work/green-bad-reviews/last.inline.json"
+echo '[]' > "$work/green-bad-reviews/last.issue.json"
+run_case "pr-reviews failure exits 6" 6 "$work/green-bad-reviews"
+
 mk "$work/red" last.json <<'EOF'
 {"headRefOid":"aaaaaaaaaaaa","mergeable":"MERGEABLE","mergeStateStatus":"UNSTABLE","statusCheckRollup":[
  {"name":"build","status":"COMPLETED","conclusion":"FAILURE"}]}