refactor(pm): fleet-roster reads the mailbox constants from mailbox-open (#25506)

Fixes #25463

Clause-②: no
Metadata-protocol: none

## What changed

- `scripts/pm/fleet-roster.mjs` no longer declares `MAILBOX_LABEL`,
`LEDGER_EXCLUSION` and `MAILBOX_BRANCH_PREFIX` itself. It imports them
from `./mailbox-open.mjs`, their one owner since #25433 landed. Its own
comment had asked for this ("once it lands, import them … and delete
these").
- No caller imported the three from `fleet-roster.mjs`; `git grep` finds
no import of that file. So nothing is re-exported.
- The self-test pins that the three values are the opener's own. The
battery "wall notes, closing refs, verdicts and mailboxes" goes 12 → 13.

## Verification

- `node scripts/pm/fleet-roster.mjs --self-test` → 69 cases in 7
batteries pass. `node scripts/pm/mailbox-open.mjs --self-test` → 40
pass.
- `git grep -n "'pm:mailbox'" -- scripts/pm`: the one declaration is in
`mailbox-open.mjs`. The other hits are test fixtures.
- `dispatch-gates --commands`: 30 derived families, all exit 0; `--ran`
→ 30 run, 0 NOT-MEASURED.
- Not governed: one file under `scripts/pm`. No changeset, because
nothing is published (`skip-changeset`).

---
_Generated by [Claude
Code](https://claude.ai/code/session_01LKHDniRQSWjRJyDtacwpEd)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: objectstack-fleet[bot]

scripts/pm/fleet-roster.mjs

@@ -86,6 +86,10 @@ import { fileURLToPath } from 'node:url';
 
 import { isEntrypoint } from '../invoked-as.mjs';
 import { validateStroke } from './fleet-write/validate.mjs';
+// The mailbox label, its ledger exclusion and its branch prefix have ONE owner,
+// the mailbox opener (#25417); this file reads them, never re-spells them.
+import * as mailboxOpen from './mailbox-open.mjs';
+import { LEDGER_EXCLUSION, MAILBOX_BRANCH_PREFIX, MAILBOX_LABEL } from './mailbox-open.mjs';
 
 const SELF_PATH = fileURLToPath(import.meta.url);
 const PM_DIR = dirname(SELF_PATH);
@@ -104,12 +108,6 @@ export const ROSTER_MARKER = '<!-- fleet-roster: generated by scripts/pm/fleet-r
 export const STALE_HOURS = 6;
 export const SUSPECTED_WALL = '疑似撞墙';
 
-// The mailbox label and its ledger exclusion are owned by `mailbox-open.mjs`
-// (#25417). Until that file is on main they are spelled here under the same
-// names; once it lands, import them from './mailbox-open.mjs' and delete these.
-export const MAILBOX_LABEL = 'pm:mailbox';
-export const LEDGER_EXCLUSION = `-label:${MAILBOX_LABEL}`;
-const MAILBOX_BRANCH_PREFIX = 'mailbox/';
 
 const CARD_BRANCH_PREFIX = 'claude/';
 const REPO_SHAPE = /^[A-Za-z0-9_.-]+\/[A-Za-z0-9_.-]+$/;
@@ -525,7 +523,7 @@ let selfTestReachedVerdict = false;
 const SELF_TEST_BATTERIES = Object.freeze({
   'arguments: modes and every refusal': 9,
   'seat titles: lane, seat, repo, status, account, project': 13,
-  'wall notes, closing refs, verdicts and mailboxes': 12,
+  'wall notes, closing refs, verdicts and mailboxes': 13,
   'the fixture snapshot: rows for the three repos': 15,
   'the rendered body: marker, columns, footer, determinism': 8,
   'refusing to overwrite what is not the roster': 6,
@@ -597,6 +595,7 @@ async function selfTest() {
   t('席位核对 with REJECT is not', hasLandingVerdict([{ body: '## 席位核对\n\nREJECT · rework' }]), false);
   t('Contract review VERDICT: PASS is a verdict', hasLandingVerdict([{ body: '## Contract review\n\nServed-tier: x\n\n**VERDICT: PASS**' }]), true);
   t('an ACCEPT outside a seat record is not', hasLandingVerdict([{ body: 'ACCEPT this please' }]), false);
+  t('the mailbox constants are the opener\'s own, imported not re-spelled', [MAILBOX_LABEL, LEDGER_EXCLUSION, MAILBOX_BRANCH_PREFIX], [mailboxOpen.MAILBOX_LABEL, mailboxOpen.LEDGER_EXCLUSION, mailboxOpen.MAILBOX_BRANCH_PREFIX]);
   t('a mailbox is read by head, then by body line; no label ⇒ none', [mailboxLogin({ labels: ['pm:mailbox'], head: { ref: 'mailbox/os-bill' } }), mailboxLogin({ labels: ['pm:mailbox'], head: { ref: 'claude/x' }, body: 'Mailbox-of: os-sales\n' }), mailboxLogin({ labels: [], head: { ref: 'mailbox/os-bill' } })], ['os-bill', 'os-sales', null]);
 
   battery('the fixture snapshot: rows for the three repos');