(MOT-4229) feat(harness): max_fires fire budget + unbounded-cron advisory

[andersonleal]

Why

rctest7 postmortem: an orchestrator registered a 10-second gate-check cron with no termination path. Its gate condition became unreachable (the reactor aggregated into mistyped tables — companion PR #592 guards that side), so the cron polled forever: 69 fires in 10 minutes until manually stopped. At 6 fires/min the fire-rate breaker (loop breaker #3) correctly never engages — this loop shape is slow, "legitimate" trigger traffic, and nothing in the platform bounded it.

What

1. metadata.max_fires: N on react bindings — a caller-declared lifetime budget of delivered fires:

• every budgeted fire is stamped __fire_seq / __fire_budget; the Nth also gets __final_fire: true + a note explaining the binding is now retired
• the final fire is delivered normally, then the binding retires through the exact once teardown path (fired records carry retired: true)
• fires past the budget (teardown raced the source / a prior unregister failed) are blocked and re-attempt teardown
• counted after gate admission, so coalesced parks don't burn budget their trailing fire will spend
• rejected on join predecessors (the join owns their lifecycle) and on once bindings with budget > 1
• counters live in the subscription registry, die with their entry, bounded for spec-hash fallback keys

2. Unbounded-cron advisory — registering a standing cron binding without a termination path appends a registration note: fires FOREVER until unregistered; set max_fires (react) and/or give the task a deadline escape (both paths: react + notify).

Tests

• unit: validate_spec budget rules, advisory variants, registry counter lifecycle (278 lib tests green)
• E2E-010 fire-budget-retires-binding: standing budgeted call-mode reaction; each fire gated on the previous call's evidence; turn 2 proves retirement via removed: false on the captured sub id before a third write is attempted; whole-run call count pins exactly 2 fires
• full integration suite: 10/10 direct scenarios pass

Fixes MOT-4229

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[github-actions]

skill-check — worker

0 verified, 48 skipped (no docs/).

Layer	Result
structure	✓
vale	✓
ai	✓
render	✓

Four for four. Nicely done.

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📥 Commits

Reviewing files that changed from the base of the PR and between 6452708 and c15898a.

📒 Files selected for processing (7)

• harness/src/functions/react.rs
• harness/src/functions/subscribe.rs
• harness/src/subscriptions/registry.rs
• harness/tests/e2e/README.md
• harness/tests/e2e/src/fixtures/tests.rs
• harness/tests/e2e/src/scenarios/fire_budget.rs
• harness/tests/e2e/src/scenarios/mod.rs

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/harness-cron-fire-budget

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