docs(devlog): open the 2.58.0 release train

devlog/_plan/260918_2580_release_train/000_roadmap.md

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+# 2.58.0 release train
+
+Open. This unit carries the 2.58.0 release from the current `dev` tip through promotion and
+publication, and records the evidence each step actually produced.
+
+## Why this unit exists
+
+The 2.58.0 line accumulated in one day: a stabilization round that closed send-budget accounting,
+third-party Responses compatibility, Cursor tool-marker and overflow handling, safe teardown and
+configuration reporting, model discovery and capacity reporting, and a dependency-audit bump, plus
+the native control stack landing behind default-off flags. That is more surface than a patch
+release, and the promotion path is the same one 2.57.0 used, so the sequence is written down before
+it runs rather than reconstructed afterwards.
+
+## Sequence
+
+| Step | Gate | Evidence to record |
+| --- | --- | --- |
+| Land the native control stack | Each layer replayed onto the current `dev`, verified byte-identical against its pre-rebase diff, flags default-off | PR numbers, exact heads, per-layer CI |
+| Freeze the candidate | `dev` tip with `package.json` at 2.58.0 | Candidate SHA, its push run |
+| Full-platform regression | `ci.yml` dispatched on the candidate with `lane=all` | All nine Windows shards individually, Linux shards, macOS legs |
+| Move `dev`'s version line | `dev-version-bump.yml` opens the bump to the next minor | Bump PR and merge commit |
+| Promote to `main` | Promotion PR from the candidate | Merge commit, `enforce-target` red by design |
+| Prove the release SHA | CI on the merge commit | Run id and conclusion |
+| Publish | `release.yml` with version, `tag=latest`, `dry-run=false`, `expected-sha` | Run id, publish line, provenance, GitHub release |
+| Promote to `preview` | Promotion PR, version line resolved to `main` | Merge commit, empty diff against `main` |
+| Registry propagation | Registry read after publish | Whether availability was confirmed or still pending |
+
+## Rules this train follows
+
+No local suite, typecheck, build, install, or `ocx` invocation is used for any gate. Every claim
+comes from hosted CI at an exact SHA. `scripts/release.ts` is not run locally for the same reason:
+its preflight runs the suite. The workflow it would dispatch is dispatched directly instead, with
+the same inputs, so the published artifact is produced by the same job.
+
+A cancelled job is not a failure and not a pass: it produced no result. Re-running it is recovery.
+Nothing is merged or published on a red gate that describes a real defect, and no budget is widened,
+retry added, or platform skipped to make a gate green.
+
+## Known open items carried into this release
+
+The contributor readiness gate holds two fork pull requests that are otherwise verified; their
+authors have the evidence and the remaining step is theirs. #4800 is not merged: the lane proved the
+provider retry policy it edits is unreachable from the Responses passthrough lane, and #4893 records
+the real defect. The native stack ships with both feature flags default-off, so an installation that
+does not opt in sees no behaviour change from it.
+