docs: release gate evidence and hold in releases.md, release_gate row in the policy key table (Step 14.5 audit)

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

docs/releases.md

@@ -29,7 +29,8 @@ it has completed and none failed, and `refs/notes/gstack-trains` holds no
 active freeze. A cancelled check run counts as red. A commit with a check run
 still going is skipped and the next older one is considered, back through 7
 days or 200 first-parent commits. The workflow runs no tests and no paid evals
-of its own; it only reads what the trains and the backstop already recorded.
+of its own; it only reads what the trains, the backstop and the release gate
+already recorded.
 With nothing green in the window it fails and lists why each commit was
 skipped.
 
@@ -54,7 +55,8 @@ contains it refuses the cut like a freeze. Train evidence relaxes nothing
 else: a red backstop run, a failed or missing `free-tests` run, any other red
 check run or a run still going keeps the commit out, and a record in any other
 state (`red`, `superseded`, `free-green`, …) is not evidence. A commit with
-neither a successful backstop run nor a train record is not released: a
+none of the three (no successful backstop run, train record or GREEN release
+record) is not released: a
 dependabot push, a policy without a train block, or a tree that was never
 gated.
 
@@ -311,11 +313,12 @@ is exercised against real check runs before it merges.
 
 | Line | Meaning |
 |---|---|
-| `CANDIDATE: <sha> (<date>) gated by main-backstop|train <nonce>` | the commit that will be (or was) released, and which evidence gated it (`[hotfix: --ref]` before `gated by` on a `--ref` cut) |
+| `CANDIDATE: <sha> (<date>) gated by main-backstop|train <nonce>|release gate run <id>` | the commit that will be (or was) released, and which evidence gated it (`[hotfix: --ref]` before `gated by` on a `--ref` cut) |
 | `NOTHING_NEW: origin/main <sha> is already released as v<X>` | nothing merged since the last release; exit 0 |
 | `NO_GREEN_COMMIT: ...` with `SKIPPED:` lines | nothing in the window passed the gate; exit 1 (a dry run exits 0: the skips are its answer) |
 | `REFUSED: non-fast-forward: ...` | the candidate is behind stable; stable only moves forward |
 | `REFUSED: queue frozen since train ...` | the main backstop froze the queue; clear it first (docs/ship-policy.md) |
+| `REFUSED: release gate red on <sha> (<cases>) and no gate on a later commit is green; ...` | the release gate's hold: land the revert or fix-forward, then `gstack-release-gate run --ignore-cadence` ([docs/ship-policy.md#release-gate](ship-policy.md#release-gate)) |
 | `REFUSED: tag v<X> already names <other sha>` | a version was stamped twice; needs a look before anything is cut |
 | `REFUSED_FLOOR: stable moved to v<X> at <time>, <h> h ago; ...` | inside the 72-hour floor; nothing changed. Exit 1 by hand, 0 on the schedule or a dry run |
 | `NEXT_ALLOWED: <time> for a hand-run cut; <time> for a scheduled run` | follows every `REFUSED_FLOOR` (and `FLOOR_UNKNOWN`, where it says why there is no time) |

docs/ship-policy.md

@@ -64,6 +64,7 @@ refuses the file (`POLICY_GSTACK_TOO_OLD`). `validate` ends with
 | `train` | `{ gate_workflow, free_workflow, full_gate_check, record_artifact, max_size, fill_hours, screen_selection, trial_reservation_usd, land? }`, `{ gates, land, max_size, fill_hours }` or `null` | `null` | Turns on [merge trains](#run-a-merge-train), read from the base revision only. Every field is required and an unknown field is `POLICY_INVALID`: `max_size` 1 to 6, `fill_hours` above 0 and at most 24, `screen_selection` `gstack-paid` \| `none`, `trial_reservation_usd` above 0 and at most 100. A block with `gates` ([any repository](#train-gates)) takes `max_size` 1 to 5 and needs `min_gstack_version` at least `TRAIN_GATES_KEY_VERSION`. `null` keeps the per-PR queue exactly as it is. Needs `min_gstack_version`. |
 | `base_red` | `{ setup, select, timeout_sec }` or `null` | `null` | How `/ship` Step 5 proves a failure is the base branch's own before pausing on it; see [base_red](#base-red). Read from the base revision only. Needs `min_gstack_version`. |
 | `changelog_fragments` | `{ dir, required_checks? }` or `null` | `null` | PRs carry unversioned [CHANGELOG fragments](#changelog-fragments) in `dir` (one flat, repo-relative directory, no `..`) and the merge step ([`land`](#land)) assigns the version. `required_checks` (up to 50 distinct names) are the checks [`train land`](#stamped-trains-under-changelog_fragments-train-land) requires present and green on a stamp commit. `null` keeps `[Unreleased]` sections and per-PR stamps. Needs `min_gstack_version`. |
+| `release_gate` | `{ cadence_hours, gate_workflow, branch, stable_ref, check_name, on_red, bisect_spend_cap_usd }` or `null` | `null` | One full paid gate on main every `cadence_hours` (8 to 168) instead of the per-push main backstop, feeding the stable release; see [release_gate](#release-gate). Every field is required: `on_red` is `hold-release`, `bisect_spend_cap_usd` 0 to 500 (0 skips the bisect). `null` keeps the per-push backstop. Needs `min_gstack_version`. |
 
 Containment, checked by `validate` and again at write time: paths and globs are
 repo-relative with no `..` segment, under 256 characters, at most 64 per list,