Normalize loop-start boundary into actual UTC

setup-rlcr-loop.sh creates loop dirs named YYYY-MM-DD_HH-MM-SS
with `date +%Y-%m-%d_%H-%M-%S` (no -u), so the basename is local
wall clock. The previous derive_loop_start_iso_ts pasted `.000Z`
on top of that basename, treating the local wall clock as if it
were already UTC. Claude transcript events carry real UTC
timestamps, so on any non-UTC machine the filter boundary was
shifted by the local offset: west-of-UTC users inherited pre-loop
background launches and stayed parked forever, east-of-UTC users
missed in-loop background work and ran Codex review too early.

Fix in hooks/lib/loop-common.sh:

  * derive_loop_start_iso_ts now does a two-step local -> epoch
    -> UTC conversion. Local wall clock is parsed into epoch
    seconds with `date -d` (GNU) or `date -j -f` (BSD/macOS),
    then the epoch is formatted in UTC as
    YYYY-MM-DDTHH:MM:SS.000Z with `date -u -d "@<epoch>"` (GNU)
    or `date -u -r <epoch>` (BSD/macOS). Any failure yields an
    empty string, which disables the filter in callers -- same
    backward-compat behaviour as before.

Regressions in tests/test-stop-hook-bg-allow.sh:

  AC-21b  pinned to `export TZ=UTC` inside its subshell so the
          expected 2026-03-01T00:00:00.000Z is TZ-deterministic.
  AC-21d  NEW. TZ=Asia/Tokyo + basename 2026-03-01_09-00-00 ->
          2026-03-01T00:00:00.000Z (9am JST = 0am UTC).
  AC-21e  NEW. TZ=America/Los_Angeles + basename
          2026-03-01_00-00-00 -> 2026-03-01T08:00:00.000Z
          (0am PST = 8am UTC; March 1 is before DST starts on
          March 8, 2026).

Validation:

  - bash tests/test-stop-hook-bg-allow.sh -> 39 passed, 0 failed
  - bash tests/run-all-tests.sh -> 1718 passed, 0 failed
  - TZ=America/Los_Angeles bash tests/test-stop-hook-bg-allow.sh
    -> 39 passed, 0 failed
  - TZ=Asia/Tokyo bash tests/test-stop-hook-bg-allow.sh
    -> 39 passed, 0 failed
  - HOME=/nonexistent/readonly bash tests/test-stop-hook-bg-allow.sh
    -> 39 passed, 0 failed

systemMessage wording unchanged. Version stays at 1.16.0.

Author: SihaoLiu

hooks/lib/loop-common.sh

@@ -268,28 +268,52 @@ extract_transcript_path() {
 }
 
 # Convert an RLCR loop dir basename to a lexically-comparable ISO-8601
-# timestamp suitable for filtering transcript events.
+# UTC timestamp suitable for filtering transcript events.
 #
-# The setup script creates loop dirs named `YYYY-MM-DD_HH-MM-SS`; real
-# Claude transcript events carry timestamps like `2026-04-16T13:19:26.819Z`.
-# String comparison works cleanly once we pad the loop boundary with
-# `.000Z` so sub-second transcript timestamps in the same second always
-# compare greater.
+# `setup-rlcr-loop.sh` creates loop dirs named `YYYY-MM-DD_HH-MM-SS` in
+# the system's LOCAL wall clock (it calls `date +%Y-%m-%d_%H-%M-%S`
+# without `-u`). Claude transcript events carry actual UTC timestamps
+# like `2026-04-16T13:19:26.819Z`. To compare them correctly, this
+# helper converts the local wall-clock parse back to a real UTC moment
+# via a two-step: parse local -> epoch seconds -> format in UTC.
+#
+# The `.000Z` suffix keeps sub-second transcript timestamps in the same
+# second compared greater via lexical string ordering.
 #
 # Usage: derive_loop_start_iso_ts "$loop_dir"
-#   Prints the ISO-8601 timestamp, or empty string when the basename does
-#   not match the expected format.
+#   Prints the ISO-8601 UTC timestamp, or empty string when the
+#   basename does not match the expected format or the local `date`
+#   binary cannot parse it.
 derive_loop_start_iso_ts() {
     local loop_dir="$1"
     local base
     base=$(basename "$loop_dir" 2>/dev/null || echo "")
-    if [[ "$base" =~ ^([0-9]{4}-[0-9]{2}-[0-9]{2})_([0-9]{2})-([0-9]{2})-([0-9]{2})$ ]]; then
-        printf '%sT%s:%s:%s.000Z' \
-            "${BASH_REMATCH[1]}" \
-            "${BASH_REMATCH[2]}" \
-            "${BASH_REMATCH[3]}" \
-            "${BASH_REMATCH[4]}"
+    if [[ ! "$base" =~ ^([0-9]{4}-[0-9]{2}-[0-9]{2})_([0-9]{2})-([0-9]{2})-([0-9]{2})$ ]]; then
+        return
+    fi
+    local local_datetime
+    local_datetime="${BASH_REMATCH[1]} ${BASH_REMATCH[2]}:${BASH_REMATCH[3]}:${BASH_REMATCH[4]}"
+
+    # Local wall-clock -> epoch seconds. GNU `date -d` first,
+    # BSD/macOS `date -j -f ...` second. Both honour the caller's TZ
+    # for interpretation, matching setup-rlcr-loop.sh's behaviour at
+    # loop-dir creation time.
+    local epoch
+    epoch=$(date -d "$local_datetime" +%s 2>/dev/null) || epoch=""
+    if [[ -z "$epoch" ]]; then
+        epoch=$(date -j -f "%Y-%m-%d %H:%M:%S" "$local_datetime" +%s 2>/dev/null) || epoch=""
+    fi
+    if [[ -z "$epoch" ]]; then
+        return
+    fi
+
+    # Epoch -> UTC ISO-8601. Try GNU then BSD.
+    local utc_iso
+    utc_iso=$(date -u -d "@$epoch" "+%Y-%m-%dT%H:%M:%S.000Z" 2>/dev/null) || utc_iso=""
+    if [[ -z "$utc_iso" ]]; then
+        utc_iso=$(date -u -r "$epoch" "+%Y-%m-%dT%H:%M:%S.000Z" 2>/dev/null) || utc_iso=""
     fi
+    printf '%s' "$utc_iso"
 }
 
 # Enumerate background-task ids that have been launched but not yet marked

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

@@ -1214,19 +1214,52 @@ else
 fi
 
 # AC-21b: confirm the derive helper produces the expected ISO-8601 form
-# so real callers get a matching boundary.
+# under TZ=UTC, where local wall clock == UTC so no offset is applied.
 AC21B_DERIVED=$(
     # shellcheck source=/dev/null
     source "$PROJECT_ROOT/hooks/lib/loop-common.sh"
+    export TZ="UTC"
     derive_loop_start_iso_ts "/tmp/.humanize/rlcr/2026-03-01_00-00-00"
 )
 if [[ "$AC21B_DERIVED" == "2026-03-01T00:00:00.000Z" ]]; then
-    pass "AC-21b: derive_loop_start_iso_ts emits ISO-8601 with .000Z suffix"
+    pass "AC-21b: derive_loop_start_iso_ts under TZ=UTC preserves the wall-clock"
 else
-    fail "AC-21b: derive_loop_start_iso_ts emits ISO-8601 with .000Z suffix" \
+    fail "AC-21b: derive_loop_start_iso_ts under TZ=UTC preserves the wall-clock" \
         "2026-03-01T00:00:00.000Z" "$AC21B_DERIVED"
 fi
 
+# AC-21d: setup-rlcr-loop.sh names the dir with local wall clock, so a
+# non-UTC caller must see the boundary shifted into actual UTC.
+# JST (UTC+9) example: 09:00 JST == 00:00 UTC.
+AC21D_DERIVED=$(
+    # shellcheck source=/dev/null
+    source "$PROJECT_ROOT/hooks/lib/loop-common.sh"
+    export TZ="Asia/Tokyo"
+    derive_loop_start_iso_ts "/tmp/.humanize/rlcr/2026-03-01_09-00-00"
+)
+if [[ "$AC21D_DERIVED" == "2026-03-01T00:00:00.000Z" ]]; then
+    pass "AC-21d: derive_loop_start_iso_ts converts JST wall-clock to correct UTC"
+else
+    fail "AC-21d: derive_loop_start_iso_ts converts JST wall-clock to correct UTC" \
+        "2026-03-01T00:00:00.000Z (9am JST = 0am UTC)" "$AC21D_DERIVED"
+fi
+
+# AC-21e: PST (UTC-8) example. Pick March 1 which is still PST (DST
+# does not start until March 8, 2026), so the offset is a fixed -8h:
+# 00:00 PST == 08:00 UTC.
+AC21E_DERIVED=$(
+    # shellcheck source=/dev/null
+    source "$PROJECT_ROOT/hooks/lib/loop-common.sh"
+    export TZ="America/Los_Angeles"
+    derive_loop_start_iso_ts "/tmp/.humanize/rlcr/2026-03-01_00-00-00"
+)
+if [[ "$AC21E_DERIVED" == "2026-03-01T08:00:00.000Z" ]]; then
+    pass "AC-21e: derive_loop_start_iso_ts converts PST wall-clock to correct UTC"
+else
+    fail "AC-21e: derive_loop_start_iso_ts converts PST wall-clock to correct UTC" \
+        "2026-03-01T08:00:00.000Z (0am PST = 8am UTC before DST)" "$AC21E_DERIVED"
+fi
+
 # AC-21c: end-to-end through the stop hook. Pre-loop launch only -> hook
 # must NOT short-circuit (no pending bg "belongs" to this loop).
 echo "Test AC-21c: stop hook ignores pre-loop launches for this loop"