This changes the codex-agent default finish flow from "merge attempt then keep" to
"wait/retry until merge succeeds, then clean merged branch/worktree".

agent-branch-finish now supports wait controls (, timeout,
poll interval) and retries PR merges until checks clear or timeout.
The template codex-agent passes wait+cleanup by default, and documentation was
updated to match the new default behavior.

Regression coverage now verifies both direct finish waiting behavior and
codex-agent end-to-end retry/cleanup behavior.

Constraint: Keep manual agent-branch-finish behavior backward compatible unless wait flags are explicit
Rejected: Force waiting for every finish invocation | would break manual async review workflows
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Codex automation should treat unresolved PR checks as incomplete work, not successful finish
Tested: npm test; node --check bin/multiagent-safety.js; npm pack --dry-run
Not-tested: Real GitHub required-check timing in external repos