CRW-603: Decide forge-only DAG targets and readerless checks

[thisisjun786]

CRW-603 chooses forge-only targets for new implementation acceptances (option C) and fail-closed comparison for a forge pull request whose merge-turn Service has no PR head reader. This PR appends the design decision and future interfaces; runtime behavior remains as built.

The comparison gives A, B and C the same four yardsticks: preserve fail-closed comparison, use recorded identity only, preserve the operating forge lane, and minimize the necessary change. It records the affected lookup predicates, test estimates, installation impact and remaining risks. C minimizes the product and persistence surface even though its fixture migration can exceed A's test delta. The follow-up is split into bounded fixture, acceptance and readerless comparison regions.

Acceptance evidence

Criterion	Evidence
c1	New section 77 of docs/port/decisions.md: baseline source anchors and two A/B/C comparison tables. Includes the in-flight hold, landed carrier, pinned target, base-refresh identity and frozen-v1 swap-gate consequences.
c2	Chooses C; rejects inference from remotes and work-report fallback. Specifies unchanged function signatures, registered refusal reasons, exact detail text (including relative/malformed-target refusal), red-first cases and implementation regions of about 600 lines or less. Product implementation is a follow-up.
c3	Validation and static checks below; full make test coverage is supplied by hosted test parts on this PR head. No contract, CLI, output-field or golden change. Existing scheduler and coordination pages describe built behavior; their updates belong to the implementation.
c4	One non-draft PR targeting dev; exact-head CI and one-shot review status are recorded below before handoff.
c5	Only docs/port/decisions.md changes. No neighbouring implementation, live-service test, production-store inspection, installation, global setting change or merge.

Verification

• go run -tags dev ./cmd/crw-dev ci validate: PASS.
• go vet ./...: PASS.
• GOOS=darwin go vet ./...: PASS.
• make lint: PASS (default/dev/integration vet, staticcheck and formatting).
• git ls-files '*.go' | xargs gofmt -l: PASS, no output.
• git diff --check: PASS.
• Docs-only prefix/scope check: PASS; the baseline document is preserved verbatim and one section is appended.
• Architect proposal and same-architect reflection: ALIGNED; independent plan/document audit recorded before publication.
• No Go package changed, so no local package tests. Local make test and go test ./... were not run, as assigned. Hosted CI covers the full suite.

Red-before/green-after: not applicable to this docs-only decision. The baseline gaps are verified from the actual comparison/acceptance branches; future behavioral regression tests are specified, not added or claimed green here.

Hosted CI: run 37253359707, pull_request, attempt 1, head c4f816c02452aa8c6036f898391f0babaae95c52: all ten jobs PASS (validate, secrets, go-product (lint), test-1 through test-4, test-rest, dist, and dev-gate). The remaining automatically triggered same-head runs are checked before the receipt. No manual rerun.

One-shot reviews: Devin completed with no findings; Codex code review completed; Codex security review skipped for usage limits. No review re-requested. Independent plan audit and fresh-reader check PASS; review-thread pagination is enumerated to the end before handoff.

Contract, scope and size

Frozen contract, refusal registry, schema, CLI, output fields and goldens: unchanged. The future slices reuse disposition_conflict and merge_target_unreadable; their behavioral/golden changes must be recorded in those implementation PRs.

Files edited outside declared region: none. Implementation: 0 lines; tests: 0 lines; documentation: 194 lines added, 0 removed; generated data: 0. No tracked blob exceeds 1 MiB.

The frozen draft predates the built head comparison. The decision also corrects an input assumption: the integration observer uses forge compare; the existing --checkout option belongs to base refresh. Latest dev is ahead; merge-tree has no conflict, so the branch is handed off without chasing dev. Coordinator refreshes its merge candidate. Source edits change no installed runtime or live operation. Coordinator owns merge and subsequent implementation.

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-05T01:58:22.368884Z	c4f816c	PR opened

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.