Fix bg task output path extraction on session resume

When a Claude Code session is resumed, the current transcript's session
id differs from the session that launched a background task, so the
task's .output file lives under the old session dir while the stop hook
probed a path derived from the new transcript. Dead/orphaned tasks were
never pruned, blocking the loop from reaching Codex review.

Teach is_bg_task_alive to extract the real output path recorded in the
transcript launch message, piping an optional transcript_path arg
through prune_dead_bg_task_ids and list_pending_background_task_ids.
Falls back to the derived tasks_dir when the transcript is unreadable or
the message is missing.

Add regression tests AC-25 (session resume) and AC-25b (whitespace in
recorded output path).

Author: SwordFaith

hooks/lib/loop-bg-tasks.sh

@@ -117,6 +117,47 @@ derive_tasks_dir_from_transcript() {
     printf '/tmp/claude-%s/%s/%s/tasks' "$uid" "$slug" "$sid"
 }
 
+# Extract the real background-task output file path recorded in the
+# transcript launch message.
+#
+# Claude Code records background Bash launches in the tool_result message
+# text as:
+#   "Command running in background with ID: <task-id>. Output is being
+#    written to: <path>. You will be notified when it completes."
+#
+# The <path> is authoritative: when a Claude session is resumed or
+# continued, the current transcript may have a different session id from
+# the session under which the task was launched, so the output file does
+# NOT live under derive_tasks_dir_from_transcript(current transcript).
+# Falling back to the derived directory causes dead/orphaned tasks to be
+# treated as alive forever.
+#
+# Usage: extract_bg_task_output_path_from_transcript "$transcript_path" "$task_id"
+#   Prints the absolute output file path, or nothing when the transcript
+#   is unreadable or the launch message does not contain a path.
+extract_bg_task_output_path_from_transcript() {
+    local transcript_path="$1" task_id="$2"
+    [[ -z "$transcript_path" ]] && return
+    [[ -f "$transcript_path" ]] || return
+    [[ -z "$task_id" ]] && return
+
+    local match
+    # Grep the JSONL line that mentions this task id and contains the
+    # literal "Output is being written to". The path is everything between
+    # that prefix and the fixed trailing sentence " You will be notified
+    # when it completes." This handles paths that contain spaces or other
+    # characters that a simple [^[:space:]]+ pattern would reject.
+    match=$(grep -F "$task_id" "$transcript_path" 2>/dev/null \
+            | grep -oE 'Output is being written to: .*\. You will be notified when it completes\.' \
+            | head -n1) || true
+    [[ -z "$match" ]] && return
+
+    local path
+    path="${match#Output is being written to: }"
+    path="${path%. You will be notified when it completes.}"
+    expand_leading_tilde "$path"
+}
+
 # Returns 0 if the background task identified by task_id appears to be alive
 # (output file absent, or lsof reports >= 1 holder), 1 if confirmed dead
 # (output file exists and lsof reports 0 holders).
@@ -127,11 +168,21 @@ derive_tasks_dir_from_transcript() {
 #
 # Set LSOF_BIN to override the lsof binary path (used in tests).
 #
-# Usage: is_bg_task_alive "$task_id" "$tasks_dir"
+# Usage: is_bg_task_alive "$task_id" "$tasks_dir" [transcript_path]
 is_bg_task_alive() {
-    local task_id="$1" tasks_dir="$2"
+    local task_id="$1" tasks_dir="$2" transcript_path="${3:-}"
     local lsof_bin="${LSOF_BIN:-lsof}"
-    local output_file="$tasks_dir/$task_id.output"
+    local output_file
+
+    # Prefer the real output path recorded in the transcript launch
+    # message; fall back to the derived tasks_dir. This matters when a
+    # Claude session has been resumed/continued and the current
+    # transcript's session id differs from the launch session id.
+    if [[ -n "$transcript_path" ]]; then
+        output_file=$(extract_bg_task_output_path_from_transcript "$transcript_path" "$task_id")
+    fi
+    [[ -n "$output_file" ]] || output_file="$tasks_dir/$task_id.output"
+
     # Output file absent -> fail open (treat as still running).
     [[ -f "$output_file" ]] || return 0
     # lsof unavailable -> fail open.
@@ -143,13 +194,13 @@ is_bg_task_alive() {
 # Filter a newline-delimited list of task IDs, retaining only those that
 # pass is_bg_task_alive. Prints surviving IDs one per line.
 #
-# Usage: prune_dead_bg_task_ids "$pending_ids" "$tasks_dir"
+# Usage: prune_dead_bg_task_ids "$pending_ids" "$tasks_dir" [transcript_path]
 prune_dead_bg_task_ids() {
-    local pending_ids="$1" tasks_dir="$2"
+    local pending_ids="$1" tasks_dir="$2" transcript_path="${3:-}"
     local task_id
     while IFS= read -r task_id; do
         [[ -z "$task_id" ]] && continue
-        is_bg_task_alive "$task_id" "$tasks_dir" && printf '%s\n' "$task_id"
+        is_bg_task_alive "$task_id" "$tasks_dir" "$transcript_path" && printf '%s\n' "$task_id"
     done <<< "$pending_ids"
 }
 
@@ -257,7 +308,7 @@ list_pending_background_task_ids() {
         local tasks_dir
         tasks_dir=$(derive_tasks_dir_from_transcript "$transcript_path")
         if [[ -n "$tasks_dir" ]]; then
-            pending=$(prune_dead_bg_task_ids "$pending" "$tasks_dir")
+            pending=$(prune_dead_bg_task_ids "$pending" "$tasks_dir" "$transcript_path")
         fi
     fi
 

tests/test-stop-hook-bg-allow.sh

@@ -237,6 +237,23 @@ emit_bg_shell_launch_result() {
         }'
 }
 
+emit_bg_shell_launch_result_with_output_path() {
+    local tool_use_id="$1" bg_task_id="$2" output_path="$3"
+    jq -c -n \
+        --arg id "$tool_use_id" \
+        --arg bid "$bg_task_id" \
+        --arg out "$output_path" \
+        '{
+          type:"user",
+          message:{
+            role:"user",
+            content:[{tool_use_id:$id, type:"tool_result",
+                      content:[{type:"text", text:("Command running in background with ID: " + $bid + ". Output is being written to: " + $out + ". You will be notified when it completes.")}]}]
+          },
+          toolUseResult:{backgroundTaskId:$bid}
+        }'
+}
+
 emit_task_completion_event() {
     local task_id="$1" tool_use_id="$2" status="${3:-completed}"
     local notif
@@ -1458,5 +1475,72 @@ run_stop_hook_with_input "$AC24_REPO" "$AC24_INPUT" "" "$TEST_DIR/bin/lsof-dead"
 rm -rf "/tmp/claude-${AC24_UID}/${AC24_SLUG}/ac24" 2>/dev/null || true
 assert_reached_codex "AC-24: dead/orphaned task (lsof no holder) is pruned; Codex review runs"
 
+# ---------------- AC-25 ----------------
+# Session resume regression: when Claude resumes a session, the current
+# transcript file has a NEW session id, but background tasks launched
+# earlier physically wrote their .output files under the OLD session
+# directory. The transcript launch message records the real path. The
+# liveness probe must look at that real path, not at a path derived
+# from the current transcript's session id, or orphaned dead tasks are
+# never pruned.
+echo "Test AC-25: liveness probe follows real output path from transcript on session resume"
+AC25_REPO="$TEST_DIR/ac25"
+create_full_fixture "$AC25_REPO" > /dev/null
+AC25_UID=$(id -u)
+AC25_SLUG=$(basename "$TRANSCRIPTS_DIR")
+AC25_OLD_SESSION="aaaaaaaa-1111-2222-3333-444444444444"
+AC25_NEW_SESSION="bbbbbbbb-5555-6666-7777-888888888888"
+AC25_TASK_ID="shell_resumed_session"
+AC25_REAL_OUTPUT="/tmp/claude-${AC25_UID}/${AC25_SLUG}/${AC25_OLD_SESSION}/tasks/${AC25_TASK_ID}.output"
+
+# Build the launch event with the real (old-session) output path embedded
+# in the Claude Code launch message.
+AC25_LAUNCH=$(emit_tool_use_assistant "toolu_AC25" "Bash" ',"command":"sleep 30"')
+AC25_RESULT=$(emit_bg_shell_launch_result_with_output_path "toolu_AC25" "$AC25_TASK_ID" "$AC25_REAL_OUTPUT")
+
+# Write the transcript under the NEW session id (resume session).
+AC25_TRANSCRIPT="/tmp/claude-${AC25_UID}/${AC25_SLUG}/${AC25_NEW_SESSION}.jsonl"
+write_transcript "$AC25_TRANSCRIPT" "$AC25_LAUNCH" "$AC25_RESULT"
+
+# The real output file lives in the OLD session directory.
+mkdir -p "$(dirname "$AC25_REAL_OUTPUT")"
+touch "$AC25_REAL_OUTPUT"
+
+AC25_INPUT=$(jq -c -n --arg tp "$AC25_TRANSCRIPT" '{transcript_path:$tp}')
+run_stop_hook_with_input "$AC25_REPO" "$AC25_INPUT" "" "$TEST_DIR/bin/lsof-dead"
+rm -rf "/tmp/claude-${AC25_UID}/${AC25_SLUG}/${AC25_OLD_SESSION}" \
+       "/tmp/claude-${AC25_UID}/${AC25_SLUG}/${AC25_NEW_SESSION}.jsonl" 2>/dev/null || true
+assert_reached_codex "AC-25: dead task pruned using real output path from transcript, not derived new-session path"
+
+# ---------------- AC-25b ----------------
+# Same as AC-25, but the recorded output path contains a space. The
+# regex used to extract the path must not stop at the first whitespace
+# token, or it will fall back to the derived new-session path and the
+# dead task will never be pruned.
+echo "Test AC-25b: liveness probe handles whitespace in recorded output path"
+AC25B_REPO="$TEST_DIR/ac25b"
+create_full_fixture "$AC25B_REPO" > /dev/null
+AC25B_UID=$(id -u)
+AC25B_SLUG=$(basename "$TRANSCRIPTS_DIR")
+AC25B_OLD_SESSION="aaaaaaaa-1111-2222-3333-444444444444"
+AC25B_NEW_SESSION="bbbbbbbb-5555-6666-7777-888888888888"
+AC25B_TASK_ID="shell_resumed_session_space"
+AC25B_REAL_OUTPUT="/tmp/claude-${AC25B_UID}/${AC25B_SLUG}/${AC25B_OLD_SESSION}/tasks/with space/${AC25B_TASK_ID}.output"
+
+AC25B_LAUNCH=$(emit_tool_use_assistant "toolu_AC25B" "Bash" ',"command":"sleep 30"')
+AC25B_RESULT=$(emit_bg_shell_launch_result_with_output_path "toolu_AC25B" "$AC25B_TASK_ID" "$AC25B_REAL_OUTPUT")
+
+AC25B_TRANSCRIPT="/tmp/claude-${AC25B_UID}/${AC25B_SLUG}/${AC25B_NEW_SESSION}.jsonl"
+write_transcript "$AC25B_TRANSCRIPT" "$AC25B_LAUNCH" "$AC25B_RESULT"
+
+mkdir -p "$(dirname "$AC25B_REAL_OUTPUT")"
+touch "$AC25B_REAL_OUTPUT"
+
+AC25B_INPUT=$(jq -c -n --arg tp "$AC25B_TRANSCRIPT" '{transcript_path:$tp}')
+run_stop_hook_with_input "$AC25B_REPO" "$AC25B_INPUT" "" "$TEST_DIR/bin/lsof-dead"
+rm -rf "/tmp/claude-${AC25B_UID}/${AC25B_SLUG}/${AC25B_OLD_SESSION}" \
+       "/tmp/claude-${AC25B_UID}/${AC25B_SLUG}/${AC25B_NEW_SESSION}.jsonl" 2>/dev/null || true
+assert_reached_codex "AC-25b: dead task pruned when real output path contains whitespace"
+
 print_test_summary "Stop Hook Background-Task Allow Test Summary"
 exit $?