fix(strategy): warn when ambiguous worktree sessions block commit linking

[peyton-alt]

https://entire.io/gh/entireio/cli/trails/940

Summary

Follow-up to #1440 for the last ask in #1852: when the sibling/parent worktree fallback finds live sessions but they span multiple worktrees, it refuses to guess — and until now the commit silently lost its Entire-Checkpoint linkage with only a DEBUG-level trace.

• Surface the refusal at WARN, listing the candidate worktrees and session count
• Message follows house style (short + factual); the candidate worktrees and session count are in structured attrs. The entire session adopt remedy stays in docs/issue guidance rather than log prose
• Test asserts the WARN lands in .entire/logs (level, message, and candidate_worktrees attr)

Terminal output was considered but the installed prepare-commit-msg and post-commit hooks intentionally redirect stderr to /dev/null, so the log-file WARN is the available surface.

Validation

• mise run fmt / mise run lint (0 issues)
• mise run test — 8377 tests green

🤖 Generated with Claude Code

---

Note

Low Risk
Observability-only: matching behavior is unchanged; adds structured WARN logging and test coverage for an existing refusal path.

Overview
When sibling/parent worktree fallback finds live sessions but they span more than one worktree, findSessionsForWorktree still returns no match (no guessing). This change emits a WARN via the checkpoint logger instead of leaving the refusal effectively invisible.

The warning lists the commit worktree, candidate session count, and distinct candidate worktrees, and tells users to run entire session adopt --from <worktree> to link a session explicitly. That targets the case where commits in a third worktree silently lose Entire-Checkpoint linkage (#1852).

A new integration test initializes logging, reproduces ambiguous sibling sessions, and asserts WARN level plus the refusal and adopt hints appear under .entire/logs (hooks redirect stderr, so logs are the intended surface).

^{Reviewed by Cursor Bugbot for commit a19d840. Configure here.}

Before / after

Captured from a real run of the ambiguous scenario (live sessions in two worktrees, git commit in a third worktree of the same repo); temp paths shortened.

Before — the only trace, visible only with log_level: DEBUG:

{"level":"DEBUG","msg":"prepare-commit-msg: no active sessions","component":"checkpoint","strategy":"manual-commit","source":"message"}

After — visible at the default level, names the worktrees involved:

{"level":"WARN","msg":"session matching: ambiguous sessions across worktrees; commit will not be linked","component":"checkpoint","commit_worktree":"/repo/.worktrees/commit","candidate_sessions":2,"candidate_worktrees":["/repo/.worktrees/first","/repo/.worktrees/second"]}
{"level":"DEBUG","msg":"prepare-commit-msg: no active sessions","component":"checkpoint","strategy":"manual-commit","source":"message"}

[Copilot]

Pull request overview

This PR improves observability for the manual-commit strategy’s worktree session matching by emitting a WARN when fallback session matching finds active sessions across multiple worktrees but refuses to guess, preventing commits from silently losing Entire-Checkpoint linkage (follow-up to #1440 / #1852).

Changes:

• Add WARN-level structured logging when ambiguous multi-worktree fallback matches are detected, including an explicit entire session adopt --from <worktree> remedy hint.
• Extend strategy worktree-session tests to assert the WARN is written to .entire/logs (since hook stderr is intentionally discarded).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cmd/entire/cli/strategy/manual_commit_session.go	Adds warnAmbiguousWorktreeSessions and calls it when fallback matching is refused due to multi-worktree ambiguity.
cmd/entire/cli/strategy/manual_commit_worktree_session_test.go	Adds a test that initializes logging, reproduces ambiguous sibling sessions, and asserts WARN-level logging plus the adopt hint in .entire/logs.