AGENTS.md amendment: same-cron wiring discipline (N=2 conversion to written rule)

Per LEARNINGS 2026-06-16/2026-06-17, convert the same-cron wiring discipline from mental rule (N=2 evidence: June 15 5-of-5 + June 16 4-of-4 same-cron POST throughput) to written AGENTS.md rule. DoD: (0) `eval "$(~/bin/gh-fleet-token.sh)"` isolated standalone-line. (a) Read current /home/agent/agents/carson-engineer/AGENTS.md. (b) Locate the appropriate insertion point — near the existing heartbeat-discipline or pre-flight section. If a section named "Nightly self-reflection ritual" or similar exists, add the new rule there; otherwise add a new section. (c) Insert the following text (or equivalent prose preserving intent): ## Same-cron wiring discipline Any state-changing reflection action item (POST, file, queue, wire, ship, send, clean, PATCH) must execute in the same cron that proposes it, OR be queued as a watchdog task with `trigger_after_utc` ≤ 12h and `due_before_utc` ≤ 18h. Prose deferrals to "next heartbeat" do not count — heartbeats have no awareness of LEARNINGS.md commitments. Items deferred without a fleet-task substrate drift indefinitely. Empirical evidence (N=2): June 15 cron POSTed 5 state-changing AIs same-cron, all 5 shipped within their windows (#12218 merge auto-completion depended on the substrate). June 16 cron POSTed 4 state-changing AIs same-cron, all 4 shipped within their windows. The June 13 reflection AI#2 (retro-POST #12218 fleet-task) was prose-deferred to "next heartbeat"; it did not ship until the June 14 cron caught the drift 24h later. Applies to: AGENTS.md amendments themselves, sub-agent task POSTs, fleet-task PATCHes, queue-for-N+2 standup tasks, watchdog tasks, default-action executor tasks, and any reflection AI containing the verbs above. (d) Save the edit; commit to local repo working tree (do not push). (e) PATCH this task to status=completed with result.diff_summary (one-line summary of inserted text), result.section_inserted (true/false), result.lines_added (count). Do NOT: open a PR for this edit unless explicitly directed by Carson. The amendment lives in the local AGENTS.md and is read by future crons; no Carson approval needed for an internal operator-discipline doc edit. No Slack DM. No outbound contact.