fix(ship-preflight): skip the base merge under queue_mode stamp-at-merge; DIFF counts the branch from its fork point

docs/ship-policy.md#ship-before-ready: under stamp-at-merge /ship never merges main into the branch (the slot stamp does). The new preflight merged origin/<base> unconditionally, so a dogfood /ship on #3633 would have merged main (crew rule 19). Failing-first test in test/ship-preflight.test.ts.

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

lib/ship-preflight.ts

@@ -7,7 +7,7 @@
  */
 import * as fs from 'node:fs';
 import * as path from 'node:path';
-import { bin, firstLine, flagReader, git, laneLine, lanes, Report, runLanes, short, sh } from './ship-bin-common';
+import { bin, firstLine, flagReader, git, laneLine, lanes, Report, runLanes, shipPolicy, short, sh } from './ship-bin-common';
 
 export const PREFLIGHT_HELP = `gstack-ship-preflight — /ship Steps 1-3 and Step 5's pregate and lanes in one call (ship/SKILL.md)
 
@@ -29,7 +29,7 @@ function integrate(cwd: string, base: string, r: Report): boolean {
   r.add(`STATUS: modified=${status.filter(l => !l.startsWith('??')).length} untracked=${status.filter(l => l.startsWith('??')).length} (uncommitted changes ship with this run)`);
   const fetch = git(cwd, ['fetch', 'origin', base], 300_000);
   if (fetch.status !== 0) { r.stop(`git fetch origin ${base} failed: ${firstLine(fetch.stderr)}; restore access first`); return false; }
-  const stat = git(cwd, ['diff', `origin/${base}`, '--shortstat']).stdout.trim();
+  const stat = git(cwd, ['diff', forkPoint(cwd, base), '--shortstat']).stdout.trim();
   const lines = [...stat.matchAll(/(\d+) (insertion|deletion)/g)].reduce((n, m) => n + Number(m[1]), 0);
   const commits = git(cwd, ['rev-list', '--count', `origin/${base}..HEAD`]).stdout.trim();
   r.add(`DIFF: ${stat || 'no changes'}; commits=${commits || 0}${lines > 200 ? '; over 200 lines: recommend /plan-eng-review or /autoplan' : ''}`);
@@ -52,19 +52,25 @@ function integrate(cwd: string, base: string, r: Report): boolean {
   return merge(cwd, base, r);
 }
 
+const forkPoint = (cwd: string, base: string) => git(cwd, ['merge-base', `origin/${base}`, 'HEAD']).stdout.trim() || `origin/${base}`;
+
 function merge(cwd: string, base: string, r: Report): boolean {
-  const before = git(cwd, ['rev-parse', 'HEAD']).stdout.trim();
-  const m = git(cwd, ['merge', `origin/${base}`, '--no-edit'], 300_000);
-  if (m.status !== 0) {
-    const conflicts = git(cwd, ['diff', '--name-only', '--diff-filter=U']).stdout.split('\n').filter(Boolean);
-    r.stop(conflicts.length
-      ? `merge conflicts in ${short(conflicts, 8)}: resolve simple ones (VERSION, schema.rb, CHANGELOG ordering) yourself; for complex or ambiguous ones ask (Step 3), then commit the merge and rerun`
-      : `git merge origin/${base} failed: ${firstLine(m.stderr || m.stdout)}`);
-    return false;
+  const policy = shipPolicy(cwd, base);
+  if (policy?.queue_mode === 'stamp-at-merge') r.add('MERGE: skipped (queue_mode stamp-at-merge: the slot stamp merges the base; docs/ship-policy.md#ship-before-ready)');
+  else {
+    const before = git(cwd, ['rev-parse', 'HEAD']).stdout.trim();
+    const m = git(cwd, ['merge', `origin/${base}`, '--no-edit'], 300_000);
+    if (m.status !== 0) {
+      const conflicts = git(cwd, ['diff', '--name-only', '--diff-filter=U']).stdout.split('\n').filter(Boolean);
+      r.stop(conflicts.length
+        ? `merge conflicts in ${short(conflicts, 8)}: resolve simple ones (VERSION, schema.rb, CHANGELOG ordering) yourself; for complex or ambiguous ones ask (Step 3), then commit the merge and rerun`
+        : `git merge origin/${base} failed: ${firstLine(m.stderr || m.stdout)}`);
+      return false;
+    }
+    const after = git(cwd, ['rev-parse', 'HEAD']).stdout.trim();
+    r.add(after === before ? 'MERGE: up to date' : `MERGE: merged origin/${base} at ${after.slice(0, 12)}`);
   }
-  const after = git(cwd, ['rev-parse', 'HEAD']).stdout.trim();
-  r.add(after === before ? 'MERGE: up to date' : `MERGE: merged origin/${base} at ${after.slice(0, 12)}`);
-  const added = git(cwd, ['diff', `origin/${base}`, '--diff-filter=A', '--name-only']).stdout.split('\n');
+  const added = git(cwd, ['diff', forkPoint(cwd, base), '--diff-filter=A', '--name-only']).stdout.split('\n');
   const untracked = git(cwd, ['ls-files', '--others', '--exclude-standard']).stdout.split('\n');
   const candidates = [...new Set([...added, ...untracked].filter(p => p && DIST.test(p)))];
   if (!candidates.length) r.add('DISTRIBUTION: no new artifact paths');
@@ -74,9 +80,7 @@ function merge(cwd: string, base: string, r: Report): boolean {
     r.add(`DISTRIBUTION: candidates=${short(candidates, 5)} release_workflow=${[...wf, ...(gitlab ? ['GITLAB_CI_RELEASE'] : [])].join(',') || 'none'}`)
       .next('Step 2: read each candidate (and manifests for new binaries or exports); a new distributable without a pipeline needs Step 2\'s question');
   }
-  const policy = bin(cwd, 'gstack-ship-policy', ['show-effective', '--base', base], 60_000).stdout;
-  const pick = (k: string) => (new RegExp(`^${k}=(\\S+)`, 'm').exec(policy)?.[1] ?? '?').replace(/^"|"$/g, '');
-  r.add(`POLICY: ${['bump', 'queue_mode', 'review_scope', 'history'].map(k => `${k}=${pick(k)}`).join(' ')} (binds Steps 12, 16 and history)`);
+  r.add(`POLICY: ${['bump', 'queue_mode', 'review_scope', 'history'].map(k => `${k}=${policy?.[k] ?? '?'}`).join(' ')} (binds Steps 12, 16 and history)`);
   const plan = bin(cwd, 'gstack-review-plan', ['--base', base, '--json'], 180_000);
   let runtime = 'unknown';
   try { runtime = String(JSON.parse(plan.stdout).runtime_lines ?? 'unknown'); } catch { /* unknown */ }

ship/SKILL.md

@@ -455,7 +455,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

ship/SKILL.md.tmpl

@@ -185,7 +185,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

test/fixtures/golden/agy-ship-SKILL.md

@@ -455,7 +455,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

test/fixtures/golden/claude-ship-SKILL.md

@@ -455,7 +455,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

test/fixtures/golden/codex-ship-SKILL.md

@@ -454,7 +454,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

test/fixtures/golden/factory-ship-SKILL.md

@@ -456,7 +456,7 @@ not web services already deployed.
 
 ## Step 3: Merge the base branch (BEFORE tests)
 
-The preflight merges the base ref it fetched (`git merge origin/<base> --no-edit`) so tests and reviews cover the integrated code (`MERGE:`).
+The preflight merges the fetched base (`git merge`) so tests and reviews cover the integrated code (`MERGE:`; `skipped` under stamp-at-merge).
 
 **Merge conflicts:** `MERGE:` names them. Auto-resolve simple ones (VERSION, schema.rb, CHANGELOG ordering). For complex or ambiguous conflicts, **STOP**, show the conflicting choices, use AskUserQuestion for the resolution, and wait for the answer before editing or continuing; then commit and rerun the preflight.
 

test/ship-preflight.test.ts

@@ -60,6 +60,20 @@ describe('gstack-ship-preflight', () => {
     expect(r.stdout).not.toContain('LANE:');
   });
 
+  // Value: protects=under queue_mode stamp-at-merge /ship never merges the base into the branch (docs/ship-policy.md#ship-before-ready; the slot stamp does), and DIFF counts only the branch's own change; fails_when=the preflight merges main anyway or DIFF counts the base's movement;
+  //   why_new=GSTA-167 dogfood on #3633 hit the merge under stamp-at-merge; seam=gstack-ship-policy show-effective; no_claim=the slot stamp's merge
+  test('queue_mode stamp-at-merge: the base is not merged and DIFF is the branch alone', () => {
+    const f = fx({ '.gstack/ship-policy.json': '{"queue_mode":"stamp-at-merge"}\n' });
+    f.advanceBase({ 'docs/new.md': '# new\n' });
+    const head = f.git('rev-parse', 'HEAD').stdout.trim();
+    const r = f.run(PREFLIGHT, ['--base', 'main']);
+    expect(r.status).toBe(0);
+    expect(lineOf(r.stdout, 'MERGE')).toMatch(/^MERGE: skipped \(queue_mode stamp-at-merge/);
+    expect(f.git('rev-parse', 'HEAD').stdout.trim()).toBe(head);
+    expect(lineOf(r.stdout, 'DIFF')).toMatch(/^DIFF: 1 file changed, 1 insertion\(\+\); commits=1$/);
+    expect(lineOf(r.stdout, 'POLICY')).toContain('queue_mode=stamp-at-merge');
+  });
+
   // Value: protects=a failing lane and a zero-run lane both stop for Step 5's triage; fails_when=exit 0 with zero tests counts as a pass, or a failure continues to Step 6;
   //   why_new=moved from Step 5's lane block; seam=gstack-evidence tests_ran; no_claim=the triage outcome
   test('a failing lane and a ZERO-RUN lane stop for Step 5 triage', () => {

test/size-ledger/ship/gsta-167-pr34.json

@@ -0,0 +1,4 @@
+{
+  "bytes": 1,
+  "why": "gstack-ship-preflight skips the base merge under queue_mode stamp-at-merge (Step 3 note)"
+}