Guard TaskStop matching against non-string messages

Coerce .toolUseResult.message with tostring before jq contains() so that unrelated tool results carrying structured messages do not error out and poison the completion pipeline under pipefail.

Adds a regression test mixing a completed background task, an SDK task_notification, and an unrelated toolUseResult whose .message is an object.

Author: SwordFaith

hooks/lib/loop-bg-tasks.sh

@@ -330,15 +330,18 @@ list_pending_background_task_ids() {
             # system event for a TaskStop. The id is read from .task_id when
             # present; otherwise it is parsed out of the message text as a
             # fallback, because some builds record the id only there. The
-            # `try ... catch empty` keeps a degenerate message (prefix with
-            # no id, so the regex cannot match) from raising and poisoning
-            # the pipefail pipeline.
+            # message is coerced with `tostring` before `contains()` because
+            # unrelated toolUseResult records may carry a structured (object,
+            # array, number) `.message`, and `contains()` errors on non-strings;
+            # without the coercion one bad record would wipe the whole `completed`
+            # set under pipefail. The `try ... catch empty` keeps a degenerate
+            # message (prefix with no id, so the regex cannot match) from raising.
             jq -r '
                 select(.toolUseResult != null)
-                | select((.toolUseResult.message // "")
-                         | contains("Successfully stopped task:"))
+                | ((.toolUseResult.message // "") | tostring) as $msg
+                | select($msg | contains("Successfully stopped task:"))
                 | (.toolUseResult.task_id
-                   // try ((.toolUseResult.message // "")
+                   // try ($msg
                          | capture("Successfully stopped task: (?<i>[^ (]+)")
                          | .i) catch empty)
             ' "$transcript_path" 2>/dev/null

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

@@ -31,6 +31,7 @@
 #   find_active_loop default ignores marker   -> validators stay isolated
 #   hook input omits session_id               -> cross-session guard fires
 #   malformed transcript with marker          -> marker preserved (fail-closed)
+#   TaskStop scan with non-string message     -> unrelated tool_result does not poison completions
 #
 
 set -euo pipefail
@@ -315,6 +316,25 @@ emit_task_stop_result_message_only() {
         }'
 }
 
+# Unrelated tool_result whose .message is a structured value rather than a
+# string. list_pending_background_task_ids scans every .toolUseResult while
+# looking for TaskStop records; a non-string .message must not make jq's
+# `contains()` error and poison the completion pipeline under pipefail.
+emit_tool_result_nonstring_message() {
+    local tool_use_id="$1"
+    jq -c -n \
+        --arg id "$tool_use_id" \
+        '{
+          type:"user",
+          message:{
+            role:"user",
+            content:[{tool_use_id:$id, type:"tool_result",
+                      content:[{type:"text", text:"structured result"}]}]
+          },
+          toolUseResult:{message:{status:"ok", details:[1,2,3]}, status:"success"}
+        }'
+}
+
 write_transcript() {
     local path="$1"
     shift
@@ -1670,6 +1690,34 @@ else
         "empty pending list" "got: $TASKSTOP_MSGONLY_HELPER_PENDING"
 fi
 
+# ---- TaskStop scan tolerates structured messages on unrelated tool_results ----
+# Source 3 iterates every .toolUseResult and calls `contains()` on .message.
+# An unrelated tool_result whose .message is an object/array/number would make
+# jq error; because the completion pipeline falls back to `completed=""`, that
+# error wipes valid SDK/legacy completions and makes completed tasks pending
+# again. The fix coerces .message to a string before `contains()`.
+echo "Test: helper tolerates non-string .message on unrelated tool_results"
+NONSTRING_MSG_REPO="$TEST_DIR/nonstring_msg"
+create_full_fixture "$NONSTRING_MSG_REPO" > /dev/null
+NONSTRING_MSG_TRANSCRIPT="$TRANSCRIPTS_DIR/nonstring_msg.jsonl"
+NONSTRING_MSG_LAUNCH=$(emit_tool_use_assistant "toolu_nonstring" "Agent" ',"description":"x","prompt":"x"')
+NONSTRING_MSG_RESULT=$(emit_async_agent_launch_result "toolu_nonstring" "agent_nonstring")
+NONSTRING_MSG_COMPLETE=$(emit_sdk_task_notification "agent_nonstring" "toolu_nonstring" "completed")
+NONSTRING_MSG_NOISE=$(emit_tool_result_nonstring_message "toolu_noise")
+write_transcript "$NONSTRING_MSG_TRANSCRIPT" "$NONSTRING_MSG_LAUNCH" "$NONSTRING_MSG_RESULT" "$NONSTRING_MSG_COMPLETE" "$NONSTRING_MSG_NOISE"
+
+NONSTRING_MSG_PENDING=$(
+    # shellcheck source=/dev/null
+    source "$PROJECT_ROOT/hooks/lib/loop-common.sh"
+    list_pending_background_task_ids "$NONSTRING_MSG_TRANSCRIPT" 2>/dev/null
+)
+if [[ -z "$NONSTRING_MSG_PENDING" ]]; then
+    pass "non-string .message on unrelated tool_result does not poison completions"
+else
+    fail "non-string .message on unrelated tool_result does not poison completions" \
+        "empty pending list" "got: $NONSTRING_MSG_PENDING"
+fi
+
 # ---- cross-session output glob: dead task pruned when transcript has no path ----
 # Fix B - cross-session output glob. On session resume the current
 # transcript has a NEW session id while the task's .output file lives