test(dag): enforce core behavior coverage

[LeXwDeX]

Summary

• run DAG core behavior suites before PRs merge to dev or main
• enforce fixed line/function floors across 16 critical DAG modules
• cover all public workflow control routes and all durable DAG manifest entries
• document the core-invariant coverage matrix and remaining design-dependent risks

TDD evidence

• coverage gate began with a missing-module red test, then passed after the minimal implementation
• deliberately misrouting cancel to pause made the public control test fail, then pass after restoration
• removing DAG manifest inventory made the canonical membership test fail, then pass after restoration
• raising loop coverage floor to 99% made the gate fail despite 399 green behavior tests

Verification

• Core: 90 passed
• OpenCode DAG: 399 passed
• Schema: 3 passed
• TUI DAG: 50 passed
• generated SDK: clean
• repository typecheck: 29/29 passed

Known boundary

Bun 1.3.14 LCOV has no branch records, so state-transition branch protection remains behavior-matrix based. Store retry/backoff stays out until its semantics are designed.