fix(cron): harden cron fixes against adversarial-review findings

Two blind adversarial reviewers found real holes in the prior cron commits:

SECURITY (was CRITICAL): the prompt-file guard was blocklist-only by default,
so promptFilePath:/proc/self/environ leaked the SERVER PROCESS's entire
environment (every secret) into the agent session, and /dev/zero or a FIFO
caused an unbounded readFile → OOM/hang DoS. A denylist is the wrong posture
for an exfil-into-LLM sink. resolveSafePromptPath now:
  - confines the realpath-resolved file to the job's working dir (ALLOWLIST) —
    closes /proc, /dev, other homes, modern cloud-cred paths, and symlink escapes
  - requires a regular file (rejects dirs/FIFOs/char devices)
  - caps the read at MAX_PROMPT_FILE_BYTES (1 MiB)
  - keeps the /etc,/root,secrets blocklist as defense-in-depth

LOGIC:
  - once-rearm (was MED, defeated in prod): the edit UI round-trips the full
    job, so the field-PRESENCE re-arm check always fired → a renamed fired
    once-job could be resurrected via edit→re-enable. Now compares schedule
    VALUES; an unchanged schedule never re-arms.
  - skipped-run history (was HIGH): recording a skip every tick was unbounded
    state.json growth. Now coalesces consecutive skips (one record per streak)
    and prunes global run history to MAX_CRON_RUN_HISTORY (500), covering the
    launch path too.
  - skip bookkeeping (was MED): a skip no longer advances lastRunAt (nothing
    ran); lastStatus still reflects 'skipped'.

Regression tests added/updated (43 pass): /proc/self/environ + outside-workspace
+ symlink-escape + non-regular + oversized all blocked, in-workspace file
passes; UI-path once resurrection blocked; consecutive skips coalesce to one
record; skip leaves lastRunAt null.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PmvZR12aX2v8K7YhqxPUAU

src/config/map-limits.ts

@@ -43,6 +43,13 @@ export const MAX_SSE_CLIENTS = 100;
  */
 export const MAX_TODOS_PER_SESSION = 500;
 
+/**
+ * Maximum cron-job run-history records retained across all jobs. Oldest runs
+ * (by startedAt) are pruned when exceeded — bounds state.json growth from
+ * frequently-firing or perpetually-skipped jobs.
+ */
+export const MAX_CRON_RUN_HISTORY = 500;
+
 // ============================================================================
 // Pending Tool Calls Limits
 // ============================================================================