fix(runway): ISS-001 reconcile stale merge retries

[sbalabanov]

Summary

Intent:

• Let at-least-once merge deliveries converge when a prior attempt already updated Git but failed to publish its result.
• Preserve staleness protection for superseded requests that would still modify the target.

Changes:

• Apply transforming merge strategies locally before staleness validation and return success when the target already satisfies every step.
• Check PROMOTE containment before freshness and account for head refs moved by a prior contention attempt.
• Add real-Git fail-once end-to-end coverage, strategy-level regression tests, and adjacent reproduction documentation.

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_{Generated by the 🪄 pr-create skill in devexp-agent-marketplace}

Test Plan

AI Verification

Validated at 935e871 on Sep 4 22:05 UTC · 5 files analyzed · 1s

Validator	Status	Issues
android-lint	not_applicable	0
java-coverage	not_applicable	0
ios-lint	not_applicable	0
web-repocheck	not_applicable	0
java-lint	not_applicable	0
go-coverage	not_applicable	0
go-gazelle	not_applicable	0
arc-lint	not_applicable	0
visual-ios	not_applicable	0
visual-android	not_applicable	0
go-proto-lint	not_applicable	0
android-coverage	not_applicable	0
arc-unit	not_applicable	0
go-thrift-lint	not_applicable	0
ios-test	not_applicable	0
uber-one	not_applicable	0
web-lint	not_applicable	0
web-coverage	not_applicable	0
diff-template	not_applicable	0
fix-disclosure	not_applicable	0
go-lint	not_applicable	0
web-typecheck	not_applicable	0
web-unit	not_applicable	0
merge-conflict	not_applicable	0
visual-web	not_applicable	0
ureview	completed	0
custom	not_applicable	0

0 issues detected

_{Skipped validators: claude · EngWiki}

Prior runs

Run at c9ee7a8 on Sep 4 22:04 UTC · 5 files · 2s · 0 issues detected

Issues

[CLAassistant]

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[sbalabanov]

Reviewed with the same lens as #678. The fix itself looks right: applying first and checking freshness only when the apply would actually change the target is the correct way to make a redelivery converge, and the terminal-vs-retryable split still holds (checkStale returns ErrInvalidRequest, the controller turns it into FAILED and acks). The e2e fail-once trigger is a genuinely good regression test.

My main comment is the one you flagged: the loop got much harder to read. Measured on git_merger.go:

	cyclomatic	max nesting
applyTransforming before	13	4
applyTransforming after	18	5

It is now the most complex function in the file (next is resolveAndValidate at 14). I tried a smaller shape, and it works — details inline.

Four smaller notes below.

_{🤖 [posted by agent] — automated review by Claude Code, requested by @sbalabanov.}