fix: thread cached merge gate inputs

[brickfrog]

Fix choir-45t3 by caching the existing poller-resolved default branch on ServerState (main until the first tick), then passing it and tracked.audit_receipt_state into the synchronous leaf disconnect merge gate. Added regression coverage for pending/findings, valid/not-required receipts, default-branch behavior, and tick cache refresh. Verification: moon test --target native (2273 passed); moon run src/bin/choir_lint --target native (passed).

Verification

Generated by Choir from commands executed in the leaf workspace.

• moon test --target native
  • exit: 0
  • head: 291fa97
  • output tail:

----- BEG5
IN MOON TEST RESULT -----
{"type":"start","file":"exec_test.mbt","index":9}
----- END MOON TEST RESULT -----
Total tests: 2273, passed: 2273, failed: 0.

• moon run src/bin/choir_lint --target native
  • exit: 0
  • head: 291fa97

[brickfrog]

Choir: GitHub Actions rollup reports all checks successful on the latest head — re-check review/merge policy on GitHub (not an approval or merge signal by itself).