docs: RED screens are not seated; QUEUE_PROOF_MISSING and POLICY_SOURCE_UNAVAILABLE name the train-command causes

Step 14.5 re-audit: ship-policy.md says train build does not seat a RED
screen and its NEXT names the build without that PR; troubleshooting.md
lists train forget, train watch, verify --screen and the scratch-branch
push under QUEUE_PROOF_MISSING, and the origin/<base> fetch under
POLICY_SOURCE_UNAVAILABLE.

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

docs/ship-policy.md

@@ -605,7 +605,8 @@ prose, and record it in the READY receipt (`screen.verdict`): `SCREEN_VERDICT:
 no verdict (its report job did not finish): `ready --screen` dispatches afresh
 instead of following it, `verify --screen` refuses it (`QUEUE_PROOF_MISSING`)
 and `train build` seats the pin unscreened, as for `NOT-RUN`. A RED screen refuses `ready` under
-either choice and is never re-dispatched at the same merge SHA
+either choice, is never re-dispatched at the same merge SHA and is not seated
+by `train build`, whose `NEXT:` names the build without that PR
 (`QUEUE_SCREEN_RED`); a run that concluded success with no slice (its route
 job found the head superseded or the plan selected nothing) is `NOT-RUN`:
 `verify --screen` refuses with `QUEUE_SCREEN_NOT_RUN`, `ready --screen`

docs/troubleshooting.md

@@ -2503,7 +2503,9 @@ or corrupt object) that `git ls-tree` cannot confirm is absent; it never falls
 through to the user-owned file. It also refuses when Bun loaded a `.env` file
 from the working directory (a bare `bun gstack-pregate`), since a branch could
 then pick the user policy: run `gstack-pregate` directly or as
-`bun --no-env-file`.
+`bun --no-env-file`. `gstack-ship-queue ready` under a train policy fetches
+`origin/<base>` first and refuses with this code, quoting git's error, when
+that fetch fails.
 
 **Fix.** `git fetch origin <base> --depth=1`, then rerun. To run against the
 branch's own file deliberately, pass `--policy-from head --allow-repo-commands`;
@@ -3834,8 +3836,13 @@ which line is not yet true.
 input does not match: the gated head is not a commit here, HEAD differs from
 the gated head beyond stamps (the gate never covered this tree), an earlier
 stamp with other inputs is unfinished, the stamp journal's head moved, or a
-gate-ahead merge could not be recomputed with `git merge-tree`. Nothing was
-written unless the `QUEUE_STAMP_REFUSED:` line says `committed=yes`.
+gate-ahead merge could not be recomputed with `git merge-tree`. The train
+commands use it too: `train forget` on a record that does not exist or on a
+train still building, running or merging, `train watch` on an unknown record,
+`verify --pr <n> --screen` on a run with no verdict to read (an INCOMPLETE or
+unreadable run), and `ready --screen` when the scratch merge branch cannot be
+pushed. Nothing was written unless the `QUEUE_STAMP_REFUSED:` line says
+`committed=yes`.
 
 **Fix.** Supply the named input (fetch the gated head, pass the current base
 sha), or regate the tree you mean to stamp. For an unfinished stamp, rerun the