fix: restore minimal long-task watchdog execution chain

state/long-task-watchdog/README.md

@@ -0,0 +1,19 @@
+# Long-task watchdog evidence
+
+This directory stores file-backed external evidence produced by `scripts/long_task_watchdog.mjs`.
+
+## Purpose
+
+The original watchdog chain had state registration but no active external executor.
+This directory is the minimal proof surface for the rebuilt execution chain:
+
+- each overdue run writes a timestamped evidence artifact
+- cron can append to `cron.log`
+- `memory/watchdog-state.json` records `lastAlertAt`
+
+## Expected files
+
+- `cron.log` — append-only stdout/stderr from cron-triggered runs
+- `<timestamp>-<watchdog-id>.json` — overdue evidence artifact per emitted interval
+
+These artifacts are meant to be machine-verifiable and safe to inspect from the repo worktree.