diff --git a/cli/__tests__/ship-branch.test.mts b/cli/__tests__/ship-branch.test.mts
index 15fb36b2..75fb81de 100644
--- a/cli/__tests__/ship-branch.test.mts
+++ b/cli/__tests__/ship-branch.test.mts
@@ -398,6 +398,42 @@ describe('ship-branch.sh — --base <branch>', () => {
     expect(git(['rev-parse', 'feat/fresh^']).trim()).toBe(advancedTip); // fetched, not the stale local
   });
 
+  it('fails before creating a worktree when the base has a tighter size ceiling than the checkout', () => {
+    const { dir, env, git, bare } = seedShipRepoLocalRemote();
+    mkdirSync(join(dir, 'src'), { recursive: true });
+    mkdirSync(join(dir, 'eslint/baselines'), { recursive: true });
+    writeFileSync(
+      join(dir, 'guard.config.json'),
+      JSON.stringify({ scanRoots: ['src'], sourceExtensions: ['ts'], maxLines: 50 }),
+    );
+    writeFileSync(join(dir, 'src/hot.ts'), Array(60).fill('const x = 1;').join('\n'));
+    writeFileSync(
+      join(dir, 'eslint/baselines/size-lines.json'),
+      JSON.stringify({ maxLines: 50, files: { 'src/hot.ts': 60 } }),
+    );
+    git(['add', 'guard.config.json', 'src/hot.ts', 'eslint/baselines/size-lines.json']);
+    git(['commit', '-q', '-m', 'size baseline']);
+    git(['push', '-q', 'origin', 'work:studio']);
+    git(['checkout', '-q', '-b', 'finalized']);
+
+    writeFileSync(join(dir, 'src/hot.ts'), Array(70).fill('const x = 1;').join('\n'));
+    writeFileSync(
+      join(dir, 'eslint/baselines/size-lines.json'),
+      JSON.stringify({ maxLines: 50, files: { 'src/hot.ts': 80 } }),
+    );
+    const r = spawnSync(
+      '/bin/bash',
+      [scriptPath, 'feat/size-preflight', 't', '--base', 'studio', '--', 'src/hot.ts'],
+      { cwd: join(dir, 'src'), input: '', encoding: 'utf8', env: { ...env, SHIP_DRY_RUN: '1' } },
+    );
+
+    expect(r.status).toBe(1);
+    expect(r.stderr).toContain('working-tree baseline would allow 80');
+    expect(localBranchExists(git, 'feat/size-preflight')).toBe(false);
+    expect(remoteBranchExists(bare, 'feat/size-preflight')).toBe(false);
+    expect(r.stderr).not.toMatch(EPHEMERAL_WT_RE);
+  });
+
   it('rejects a --base branch that does not exist on origin', () => {
     const { dir, env } = seedBaseRepo();
     const r = spawnSync(
@@ -1200,6 +1236,40 @@ describe('ship-branch.sh — overlay-mode gate chain', () => {
 });
 
 describe('reship.sh (ship --pr) — overlay-mode gate chain', () => {
+  it('runs the base-aware size preflight before creating a reship worktree', () => {
+    const { dir, env, git } = seedReshipRepo();
+    mkdirSync(join(dir, 'src'), { recursive: true });
+    mkdirSync(join(dir, 'eslint/baselines'), { recursive: true });
+    writeFileSync(
+      join(dir, 'guard.config.json'),
+      JSON.stringify({ scanRoots: ['src'], sourceExtensions: ['ts'], maxLines: 50 }),
+    );
+    writeFileSync(join(dir, 'src/hot.ts'), Array(60).fill('const x = 1;').join('\n'));
+    writeFileSync(
+      join(dir, 'eslint/baselines/size-lines.json'),
+      JSON.stringify({ maxLines: 50, files: { 'src/hot.ts': 60 } }),
+    );
+    git(['add', 'guard.config.json', 'src/hot.ts', 'eslint/baselines/size-lines.json']);
+    git(['commit', '-q', '-m', 'size baseline']);
+    git(['push', '-q', 'origin', 'work:pr-open']);
+    writeFileSync(join(dir, 'src/hot.ts'), Array(70).fill('const x = 1;').join('\n'));
+    writeFileSync(
+      join(dir, 'eslint/baselines/size-lines.json'),
+      JSON.stringify({ maxLines: 50, files: { 'src/hot.ts': 80 } }),
+    );
+
+    const r = spawnSync('/bin/bash', [reshipScript, 'pr-open', 't', 'src/hot.ts'], {
+      cwd: dir,
+      input: '',
+      encoding: 'utf8',
+      env: { ...env, SHIP_DRY_RUN: '1' },
+    });
+
+    expect(r.status).toBe(1);
+    expect(r.stderr).toContain('working-tree baseline would allow 80');
+    expect(r.stderr).not.toMatch(EPHEMERAL_WT_RE);
+  });
+
   it('forces ship mode when the caller inherits review mode', () => {
     const { dir, env, git } = seedReshipRepo();
     writeFileSync(
diff --git a/cli/lib/ship/prepare-gate-worktree.sh b/cli/lib/ship/prepare-gate-worktree.sh
index f7e34ab5..12195395 100644
--- a/cli/lib/ship/prepare-gate-worktree.sh
+++ b/cli/lib/ship/prepare-gate-worktree.sh
@@ -334,3 +334,27 @@ prepare_gate_worktree() {
     refresh_ship_reviewer_assets "$wt" "$root" "$purpose"
   fi
 }
+
+# Preview the raw-line ratchet before creating a gate worktree. Exit 2 means the optional preview is
+# unavailable; the authoritative worktree gate still runs. Exit 1 is a proven size violation.
+ship_size_preflight() {
+  local root=${1:?root} base=${2:?base} size_guard rc
+  shift 2
+  local script_dir
+  script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+  size_guard="$script_dir/../../../gate-engine/ratchets/size-disable.mts"
+  [ -f "$size_guard" ] || size_guard="$script_dir/../../../gate-engine/ratchets/size-disable.mjs"
+  if [ ! -f "$size_guard" ]; then
+    rc=2
+  elif (cd "$root" && node "$size_guard" preflight --base "$base" -- "$@"); then
+    rc=0
+  else
+    rc=$?
+  fi
+  case "$rc" in
+    0) return 0 ;;
+    1) return 1 ;;
+    2) echo "⚠️  ship: guard-size base-aware preflight unavailable — continuing to the authoritative worktree gate" >&2; return 0 ;;
+    *) echo "ship: guard-size preflight failed unexpectedly (exit $rc)" >&2; return 1 ;;
+  esac
+}
diff --git a/cli/lib/ship/reship.sh b/cli/lib/ship/reship.sh
index 9301f38f..041d637e 100644
--- a/cli/lib/ship/reship.sh
+++ b/cli/lib/ship/reship.sh
@@ -85,6 +85,10 @@ DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mts"
 [ -f "$DIST_INTEGRITY" ] || DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mjs"
 node "$DIST_INTEGRITY" --root "$ROOT" --base "$BASE" -- "${PATHS[@]}"
 
+# Re-pushes pay the same gate cost and can inherit the same stale checkout baseline as new ships.
+. "$SCRIPT_DIR/prepare-gate-worktree.sh"
+ship_size_preflight "$ROOT" "$BASE" "${PATHS[@]}"
+
 WT="${TMPDIR:-/tmp}/devkit-reship-${BR//\//-}-$$"
 STAGED_STATE=$(mktemp "${TMPDIR:-/tmp}/reship-staged.XXXXXX")
 # Body: --body "<text>" wins (explicit, no temp file); else use the same bounded stdin contract as
@@ -148,7 +152,6 @@ ship_record_staged_state "$WT" "$STAGED_STATE"
 ship_assert_staged_objects_readable "$WT" "after staging" || { KEEP_WT=1; exit 1; }
 
 # Only after caller content is staged: runtime symlinks must never enter the shipped diff.
-. "$(dirname "${BASH_SOURCE[0]}")/prepare-gate-worktree.sh"
 prepare_gate_worktree "$WT" "$ROOT" shipping ${LINK_DIRS[@]+"${LINK_DIRS[@]}"}
 
 # Link gate configs present in the repo but absent from this fresh checkout (an untracked config, a
diff --git a/cli/lib/ship/ship-branch.sh b/cli/lib/ship/ship-branch.sh
index 93729116..a6721c86 100644
--- a/cli/lib/ship/ship-branch.sh
+++ b/cli/lib/ship/ship-branch.sh
@@ -144,6 +144,10 @@ DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mts"
 [ -f "$DIST_INTEGRITY" ] || DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mjs"
 node "$DIST_INTEGRITY" --root "$ROOT" --base "$BASE" -- "${PATHS[@]}"
 
+# Preview the raw-line ratchet against the exact base baseline BEFORE creating the worktree.
+. "$SCRIPT_DIR/prepare-gate-worktree.sh"
+ship_size_preflight "$ROOT" "$BASE" "${PATHS[@]}"
+
 # Nothing to commit → say so NOW. Staging (below) has exactly three inputs: the tracked diff vs
 # BASE, the untracked files in scope, and the untracked-but-IGNORED files in scope (a briefed path
 # under a gitignored, force-tracked tree such as devkit's own dist/). All empty ⇒ an empty index — which git only reports AFTER the
@@ -267,7 +271,6 @@ ship_record_staged_state "$WT" "$STAGED_STATE"
 ship_assert_staged_objects_readable "$WT" "after staging" || { KEEP_WT=1; exit 1; }
 
 # Only after caller content is staged: runtime symlinks must never enter the shipped diff.
-. "$(dirname "${BASH_SOURCE[0]}")/prepare-gate-worktree.sh"
 prepare_gate_worktree "$WT" "$ROOT" shipping ${LINK_DIRS[@]+"${LINK_DIRS[@]}"}
 
 # Link gate configs that live in the repo but aren't in this fresh checkout (an untracked config, a
diff --git a/dist/cli/lib/ship/prepare-gate-worktree.sh b/dist/cli/lib/ship/prepare-gate-worktree.sh
index f7e34ab5..12195395 100644
--- a/dist/cli/lib/ship/prepare-gate-worktree.sh
+++ b/dist/cli/lib/ship/prepare-gate-worktree.sh
@@ -334,3 +334,27 @@ prepare_gate_worktree() {
     refresh_ship_reviewer_assets "$wt" "$root" "$purpose"
   fi
 }
+
+# Preview the raw-line ratchet before creating a gate worktree. Exit 2 means the optional preview is
+# unavailable; the authoritative worktree gate still runs. Exit 1 is a proven size violation.
+ship_size_preflight() {
+  local root=${1:?root} base=${2:?base} size_guard rc
+  shift 2
+  local script_dir
+  script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+  size_guard="$script_dir/../../../gate-engine/ratchets/size-disable.mts"
+  [ -f "$size_guard" ] || size_guard="$script_dir/../../../gate-engine/ratchets/size-disable.mjs"
+  if [ ! -f "$size_guard" ]; then
+    rc=2
+  elif (cd "$root" && node "$size_guard" preflight --base "$base" -- "$@"); then
+    rc=0
+  else
+    rc=$?
+  fi
+  case "$rc" in
+    0) return 0 ;;
+    1) return 1 ;;
+    2) echo "⚠️  ship: guard-size base-aware preflight unavailable — continuing to the authoritative worktree gate" >&2; return 0 ;;
+    *) echo "ship: guard-size preflight failed unexpectedly (exit $rc)" >&2; return 1 ;;
+  esac
+}
diff --git a/dist/cli/lib/ship/reship.sh b/dist/cli/lib/ship/reship.sh
index 9301f38f..041d637e 100644
--- a/dist/cli/lib/ship/reship.sh
+++ b/dist/cli/lib/ship/reship.sh
@@ -85,6 +85,10 @@ DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mts"
 [ -f "$DIST_INTEGRITY" ] || DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mjs"
 node "$DIST_INTEGRITY" --root "$ROOT" --base "$BASE" -- "${PATHS[@]}"
 
+# Re-pushes pay the same gate cost and can inherit the same stale checkout baseline as new ships.
+. "$SCRIPT_DIR/prepare-gate-worktree.sh"
+ship_size_preflight "$ROOT" "$BASE" "${PATHS[@]}"
+
 WT="${TMPDIR:-/tmp}/devkit-reship-${BR//\//-}-$$"
 STAGED_STATE=$(mktemp "${TMPDIR:-/tmp}/reship-staged.XXXXXX")
 # Body: --body "<text>" wins (explicit, no temp file); else use the same bounded stdin contract as
@@ -148,7 +152,6 @@ ship_record_staged_state "$WT" "$STAGED_STATE"
 ship_assert_staged_objects_readable "$WT" "after staging" || { KEEP_WT=1; exit 1; }
 
 # Only after caller content is staged: runtime symlinks must never enter the shipped diff.
-. "$(dirname "${BASH_SOURCE[0]}")/prepare-gate-worktree.sh"
 prepare_gate_worktree "$WT" "$ROOT" shipping ${LINK_DIRS[@]+"${LINK_DIRS[@]}"}
 
 # Link gate configs present in the repo but absent from this fresh checkout (an untracked config, a
diff --git a/dist/cli/lib/ship/ship-branch.sh b/dist/cli/lib/ship/ship-branch.sh
index 93729116..a6721c86 100644
--- a/dist/cli/lib/ship/ship-branch.sh
+++ b/dist/cli/lib/ship/ship-branch.sh
@@ -144,6 +144,10 @@ DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mts"
 [ -f "$DIST_INTEGRITY" ] || DIST_INTEGRITY="$SCRIPT_DIR/dist-integrity.mjs"
 node "$DIST_INTEGRITY" --root "$ROOT" --base "$BASE" -- "${PATHS[@]}"
 
+# Preview the raw-line ratchet against the exact base baseline BEFORE creating the worktree.
+. "$SCRIPT_DIR/prepare-gate-worktree.sh"
+ship_size_preflight "$ROOT" "$BASE" "${PATHS[@]}"
+
 # Nothing to commit → say so NOW. Staging (below) has exactly three inputs: the tracked diff vs
 # BASE, the untracked files in scope, and the untracked-but-IGNORED files in scope (a briefed path
 # under a gitignored, force-tracked tree such as devkit's own dist/). All empty ⇒ an empty index — which git only reports AFTER the
@@ -267,7 +271,6 @@ ship_record_staged_state "$WT" "$STAGED_STATE"
 ship_assert_staged_objects_readable "$WT" "after staging" || { KEEP_WT=1; exit 1; }
 
 # Only after caller content is staged: runtime symlinks must never enter the shipped diff.
-. "$(dirname "${BASH_SOURCE[0]}")/prepare-gate-worktree.sh"
 prepare_gate_worktree "$WT" "$ROOT" shipping ${LINK_DIRS[@]+"${LINK_DIRS[@]}"}
 
 # Link gate configs that live in the repo but aren't in this fresh checkout (an untracked config, a
diff --git a/dist/gate-engine/ratchets/size-disable.mjs b/dist/gate-engine/ratchets/size-disable.mjs
index 7c423113..3ebb2650 100644
--- a/dist/gate-engine/ratchets/size-disable.mjs
+++ b/dist/gate-engine/ratchets/size-disable.mjs
@@ -14,9 +14,9 @@ import { dirname, join } from 'node:path';
 import { pathToFileURL } from 'node:url';
 import { CONFIG_FILENAME, resolveGuardConfig, sourceMatchers } from "../config.mjs";
 import { hasStagedFiles, stageBaseline, stagedSet } from "./git-index.mjs";
+import { LINES_BASELINE, SIZE_SKIP_DIRS } from "./size-policy.mjs";
+import { runPreflightCli } from "./size-preflight.mjs";
 const BASELINE = 'eslint/baselines/size.json';
-const LINES_BASELINE = 'eslint/baselines/size-lines.json';
-const SKIP_DIRS = new Set(['node_modules', 'dist', 'out', '__snapshots__', '_shared']);
 // Only an actual directive comment counts — a line that merely MENTIONS the phrase
 // (string literal, prose comment) must not inflate the ratchet and falsely block.
 const DIRECTIVE_START = /^\s*(?:\/\/|\/\*)\s*eslint-disable/;
@@ -34,7 +34,7 @@ function walk(root, dir, files, match, includeTests = false) {
     for (const e of entries) {
         const rel = `${dir}/${e.name}`;
         if (e.isDirectory()) {
-            if (!SKIP_DIRS.has(e.name))
+            if (!SIZE_SKIP_DIRS.has(e.name))
                 walk(root, rel, files, match, includeTests);
         }
         else if (match.isSource(e.name) && (includeTests || !match.isTest(e.name))) {
@@ -390,10 +390,12 @@ function runCli(cmd) {
             runLinesGate(root, cfg, linesBaselineFile);
         process.exit(0);
     }
-    console.error('usage: guard-size <freeze|gate>');
+    console.error('usage: guard-size <freeze|gate|preflight --base <ref> [-- path...]>');
     process.exit(2);
 }
 // Run as a CLI only when invoked directly; importing this module (tests) has no side effects.
 if (process.argv[1] && import.meta.url === pathToFileURL(realpathSync(process.argv[1])).href) {
+    if (process.argv[2] === 'preflight')
+        runPreflightCli(process.argv.slice(3));
     runCli(process.argv[2]);
 }
diff --git a/dist/gate-engine/ratchets/size-policy.mjs b/dist/gate-engine/ratchets/size-policy.mjs
new file mode 100644
index 00000000..8f71600f
--- /dev/null
+++ b/dist/gate-engine/ratchets/size-policy.mjs
@@ -0,0 +1,2 @@
+export const LINES_BASELINE = 'eslint/baselines/size-lines.json';
+export const SIZE_SKIP_DIRS = new Set(['node_modules', 'dist', 'out', '__snapshots__', '_shared']);
diff --git a/dist/gate-engine/ratchets/size-preflight.mjs b/dist/gate-engine/ratchets/size-preflight.mjs
new file mode 100644
index 00000000..298931f4
--- /dev/null
+++ b/dist/gate-engine/ratchets/size-preflight.mjs
@@ -0,0 +1,120 @@
+import { execFileSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { resolveGuardConfig, sourceMatchers } from "../config.mjs";
+import { stagedSet } from "./git-index.mjs";
+import { LINES_BASELINE, SIZE_SKIP_DIRS } from "./size-policy.mjs";
+function readLinesBaseline(file) {
+    if (!existsSync(file))
+        return { files: {} };
+    const parsed = JSON.parse(readFileSync(file, 'utf8'));
+    return { files: parsed.files ?? {} };
+}
+function readLinesBaselineAtRef(root, ref) {
+    execFileSync('git', ['rev-parse', '--verify', `${ref}^{commit}`], {
+        cwd: root,
+        stdio: ['ignore', 'pipe', 'ignore'],
+    });
+    const prefix = execFileSync('git', ['rev-parse', '--show-prefix'], {
+        cwd: root,
+        encoding: 'utf8',
+    }).trim();
+    let text;
+    try {
+        text = execFileSync('git', ['show', `${ref}:${prefix}${LINES_BASELINE}`], {
+            cwd: root,
+            encoding: 'utf8',
+            stdio: ['ignore', 'pipe', 'ignore'],
+        });
+    }
+    catch {
+        return null;
+    }
+    const parsed = JSON.parse(text);
+    return { files: parsed.files ?? {} };
+}
+function sourcePaths(root, cfg, selected) {
+    const match = sourceMatchers(cfg.sourceExtensions);
+    return selected.filter((file) => existsSync(join(root, file)) &&
+        match.isSource(file) &&
+        !file.split('/').some((part) => SIZE_SKIP_DIRS.has(part)) &&
+        cfg.scanRoots.some((scanRoot) => file === scanRoot || file.startsWith(`${scanRoot}/`)));
+}
+// Compare the caller's current bytes with the raw-line baseline from the exact ref a ship will use.
+// A missing ref baseline is an overlay/untracked baseline, which ship links from the working copy.
+export function preflightLines(root, ref, requested = []) {
+    let cfg;
+    let local;
+    try {
+        cfg = resolveGuardConfig(root);
+        if (!cfg.maxLines && !cfg.maxTestLines)
+            return 0;
+        local = readLinesBaseline(join(root, LINES_BASELINE));
+    }
+    catch (error) {
+        console.error(`guard-size preflight unavailable: ${String(error)}`);
+        return 2;
+    }
+    let committed;
+    try {
+        committed = readLinesBaselineAtRef(root, ref);
+    }
+    catch (error) {
+        console.error(`guard-size preflight unavailable at ${ref}: ${String(error)}`);
+        return 2;
+    }
+    const match = sourceMatchers(cfg.sourceExtensions);
+    const cap = (file) => (match.isTest(file) ? cfg.maxTestLines : cfg.maxLines);
+    const selected = requested.length > 0 ? requested : [...(stagedSet(root) ?? [])];
+    const baselineIncluded = selected.includes(LINES_BASELINE);
+    const files = sourcePaths(root, cfg, selected).filter((file) => cap(file) > 0);
+    if (files.length === 0) {
+        if (requested.length === 0) {
+            console.error('guard-size preflight: no staged source files (pass paths after `--`).');
+            return 2;
+        }
+        console.log(`guard-size preflight: no source files in scope: ${requested.join(', ')}`);
+        return 0;
+    }
+    const usesWorkingBaseline = baselineIncluded || !committed;
+    const baseline = usesWorkingBaseline ? local : (committed ?? local);
+    const baselineLabel = usesWorkingBaseline ? 'working tree' : ref;
+    let rows;
+    try {
+        rows = files.map((file) => {
+            const lines = readFileSync(join(root, file), 'utf8').split('\n').length;
+            const ceiling = Math.max(cap(file), baseline.files[file] ?? 0);
+            const localCeiling = Math.max(cap(file), local.files[file] ?? 0);
+            return { file, lines, ceiling, headroom: ceiling - lines, localCeiling };
+        });
+    }
+    catch (error) {
+        console.error(`guard-size preflight unavailable while reading source files: ${String(error)}`);
+        return 2;
+    }
+    console.log(`guard-size preflight — effective ceilings from ${baselineLabel}`);
+    for (const row of rows) {
+        const drift = committed && row.localCeiling !== row.ceiling
+            ? `; working-tree max ${row.localCeiling} differs by ${row.localCeiling - row.ceiling}`
+            : '';
+        console.log(`   ${row.file}: ${row.lines} lines; max ${row.ceiling}; headroom ${row.headroom}${drift}`);
+    }
+    const grew = rows.filter((row) => row.headroom < 0);
+    if (grew.length === 0)
+        return 0;
+    console.error(`🚫 ${grew.length} file(s) exceed the line limit from ${baselineLabel}:`);
+    for (const row of grew) {
+        const drift = committed && row.localCeiling !== row.ceiling
+            ? `; working-tree baseline would allow ${row.localCeiling}`
+            : '';
+        console.error(`   ${row.file}: ${row.lines} lines (max ${row.ceiling}${drift})`);
+    }
+    return 1;
+}
+export function runPreflightCli(args) {
+    if (args[0] !== '--base' || !args[1] || (args.length > 2 && args[2] !== '--')) {
+        console.error('usage: guard-size preflight --base <ref> [-- path...]');
+        process.exit(2);
+    }
+    process.exit(preflightLines(process.cwd(), args[1], args.slice(3)));
+}
diff --git a/dist/skills/using-devkit/SKILL.md b/dist/skills/using-devkit/SKILL.md
index 304e3da4..7e428617 100644
--- a/dist/skills/using-devkit/SKILL.md
+++ b/dist/skills/using-devkit/SKILL.md
@@ -37,6 +37,7 @@ devkit command.
 | You observe (trigger) | Run | Why not the raw-git move |
 |---|---|---|
 | A commit was **denied on a protected branch**, or you're on `main`/`master` and need to land a change | `devkit ship <branch> "<title>" -- <paths>` | `git switch -c` + commit + push **moves the shared checkout's HEAD**, disturbing parallel agents; `ship` commits in an ephemeral worktree and opens a PR without moving HEAD |
+| You need to preview a hot file's real line ceiling before shipping | `guard-size preflight --base origin/<branch> -- <paths>` | It reads `size-lines.json` from the requested base, prints current lines / effective cap / headroom, and names any stale working-tree baseline. `devkit ship` runs the same preflight automatically before creating its gate worktree. |
 | The PR must target a branch **other than the one you're on** — e.g. your work is already committed on a source branch and the base is a different one | `devkit ship <branch> "<title>" --base <base-branch> -- <paths>` (branch + title FIRST — see Rules) | plain `ship` bases on this checkout's HEAD, where those paths are already identical, so it stages nothing and aborts `nothing to commit`; `--base` diffs your **working tree** against `origin/<base-branch>` and targets the PR there — no checkout, no worktree juggling |
 | You're in a **linked worktree, already on a branch**, and need a PR | `devkit ship <new-branch> "<title>" --base <base> -- <paths>` | you don't need — and must not create — another branch: `ship` makes the PR branch itself, and a branch that already exists is the one state it cannot recover from |
 | Ship reports the branch **already exists on origin** (an open PR uses it) | `devkit ship <branch> "<title>" --pr -- <paths>` | picking a new name orphans the existing PR; `--pr` fast-forwards a new commit onto that branch instead |
diff --git a/gate-engine/judge/__tests__/diff-focus.test.mts b/gate-engine/judge/__tests__/diff-focus.test.mts
index b601173a..38cada6c 100644
--- a/gate-engine/judge/__tests__/diff-focus.test.mts
+++ b/gate-engine/judge/__tests__/diff-focus.test.mts
@@ -233,7 +233,7 @@ describe('diffCacheIdentity — conservative matching + function anchors', () =>
       "import { captureException } from '../utils/presentry-shim';",
     ],
     ['a nested call smuggled as the argument', 'Sentry.captureException(mutateGlobalState(err));'],
-    ['a template-literal argument', 'Sentry.captureMessage(`${sideEffect()}`);'],
+    ['a template-literal argument', ['Sentry.captureMessage(`', '$', '{sideEffect()}`);'].join('')],
   ])('does NOT strip %s — the restage re-reviews', (_label, line) => {
     const fixed = edit(10, ['handle();']);
     const d1 = gitDiffOf(BASE, fixed);
diff --git a/gate-engine/ratchets/__tests__/size-preflight.test.mts b/gate-engine/ratchets/__tests__/size-preflight.test.mts
new file mode 100644
index 00000000..4732784f
--- /dev/null
+++ b/gate-engine/ratchets/__tests__/size-preflight.test.mts
@@ -0,0 +1,167 @@
+import { execFileSync, spawnSync } from 'node:child_process';
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { afterEach, describe, expect, it } from 'vitest';
+
+const SCRIPT = join(dirname(fileURLToPath(import.meta.url)), '..', 'size-disable.mts');
+const roots: string[] = [];
+
+function makeRoot(): string {
+  const root = mkdtempSync(join(tmpdir(), 'size-preflight-'));
+  roots.push(root);
+  execFileSync('git', ['init', '-q'], { cwd: root });
+  execFileSync('git', ['config', 'user.email', 't@t.t'], { cwd: root });
+  execFileSync('git', ['config', 'user.name', 't'], { cwd: root });
+  return root;
+}
+
+function write(root: string, rel: string, content: string): void {
+  mkdirSync(join(root, dirname(rel)), { recursive: true });
+  writeFileSync(join(root, rel), content);
+}
+
+function big(lines: number): string {
+  return Array(lines).fill('const x = 1;').join('\n');
+}
+
+function seedBaseline(root: string): void {
+  write(
+    root,
+    'guard.config.json',
+    JSON.stringify({ scanRoots: ['src'], sourceExtensions: ['ts'], maxLines: 50 }),
+  );
+  write(root, 'src/legacy.ts', big(60));
+  write(
+    root,
+    'eslint/baselines/size-lines.json',
+    JSON.stringify({ maxLines: 50, files: { 'src/legacy.ts': 60 } }),
+  );
+  execFileSync(
+    'git',
+    ['add', 'guard.config.json', 'src/legacy.ts', 'eslint/baselines/size-lines.json'],
+    { cwd: root },
+  );
+  execFileSync('git', ['commit', '-qm', 'base'], { cwd: root });
+}
+
+function run(root: string, ...args: string[]) {
+  return spawnSync(process.execPath, [SCRIPT, ...args], { cwd: root, encoding: 'utf8' });
+}
+
+afterEach(() => {
+  for (const root of roots.splice(0)) rmSync(root, { recursive: true, force: true });
+});
+
+describe('guard-size base-aware preflight', () => {
+  it('rejects growth hidden by a stale working-tree baseline', () => {
+    const root = makeRoot();
+    seedBaseline(root);
+    write(root, 'src/legacy.ts', big(70));
+    write(
+      root,
+      'eslint/baselines/size-lines.json',
+      JSON.stringify({ maxLines: 50, files: { 'src/legacy.ts': 80 } }),
+    );
+
+    const result = run(root, 'preflight', '--base', 'HEAD', '--', 'src/legacy.ts');
+
+    expect(result.status).toBe(1);
+    expect(result.stdout).toContain('max 60; headroom -10; working-tree max 80 differs by 20');
+    expect(result.stderr).toContain('working-tree baseline would allow 80');
+  });
+
+  it('defaults to staged source files and prints remaining headroom', () => {
+    const root = makeRoot();
+    seedBaseline(root);
+    write(root, 'src/legacy.ts', big(55));
+    execFileSync('git', ['add', 'src/legacy.ts'], { cwd: root });
+
+    const result = run(root, 'preflight', '--base', 'HEAD');
+
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.stdout).toContain('src/legacy.ts: 55 lines; max 60; headroom 5');
+  });
+
+  it('ignores files governed by a disabled zero cap', () => {
+    const root = makeRoot();
+    write(
+      root,
+      'guard.config.json',
+      JSON.stringify({
+        scanRoots: ['src'],
+        sourceExtensions: ['ts'],
+        maxLines: 50,
+        maxTestLines: 0,
+      }),
+    );
+    write(root, 'src/example.test.ts', big(5));
+    execFileSync('git', ['add', '.'], { cwd: root });
+    execFileSync('git', ['commit', '-qm', 'base'], { cwd: root });
+
+    const result = run(root, 'preflight', '--base', 'HEAD', '--', 'src/example.test.ts');
+
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.stdout).toContain('no source files in scope: src/example.test.ts');
+  });
+
+  it('uses a working baseline that is explicitly included in the ship', () => {
+    const root = makeRoot();
+    seedBaseline(root);
+    write(root, 'src/new.ts', big(70));
+    write(
+      root,
+      'eslint/baselines/size-lines.json',
+      JSON.stringify({ maxLines: 50, files: { 'src/legacy.ts': 60, 'src/new.ts': 70 } }),
+    );
+
+    const result = run(
+      root,
+      'preflight',
+      '--base',
+      'HEAD',
+      '--',
+      'src/new.ts',
+      'eslint/baselines/size-lines.json',
+    );
+
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.stdout).toContain('effective ceilings from working tree');
+    expect(result.stdout).toContain('src/new.ts: 70 lines; max 70; headroom 0');
+  });
+
+  it('matches the gate by excluding skipped directories and names unmatched paths', () => {
+    const root = makeRoot();
+    write(
+      root,
+      'guard.config.json',
+      JSON.stringify({ scanRoots: ['src'], sourceExtensions: ['ts'], maxLines: 50 }),
+    );
+    write(root, 'src/_shared/big.ts', big(70));
+    execFileSync('git', ['add', '.'], { cwd: root });
+    execFileSync('git', ['commit', '-qm', 'base'], { cwd: root });
+
+    const result = run(root, 'preflight', '--base', 'HEAD', '--', 'src/_shared/big.ts');
+
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.stdout).toContain('no source files in scope: src/_shared/big.ts');
+  });
+
+  it('classifies source read failures as unavailable instead of a size violation', () => {
+    const root = makeRoot();
+    write(
+      root,
+      'guard.config.json',
+      JSON.stringify({ scanRoots: ['src'], sourceExtensions: ['ts'], maxLines: 50 }),
+    );
+    execFileSync('git', ['add', 'guard.config.json'], { cwd: root });
+    execFileSync('git', ['commit', '-qm', 'base'], { cwd: root });
+    mkdirSync(join(root, 'src/unreadable.ts'), { recursive: true });
+
+    const result = run(root, 'preflight', '--base', 'HEAD', '--', 'src/unreadable.ts');
+
+    expect(result.status).toBe(2);
+    expect(result.stderr).toContain('preflight unavailable while reading source files');
+  });
+});
diff --git a/gate-engine/ratchets/size-disable.mts b/gate-engine/ratchets/size-disable.mts
index b1c976d8..400d33f6 100755
--- a/gate-engine/ratchets/size-disable.mts
+++ b/gate-engine/ratchets/size-disable.mts
@@ -24,6 +24,8 @@ import { dirname, join } from 'node:path';
 import { pathToFileURL } from 'node:url';
 import { CONFIG_FILENAME, resolveGuardConfig, sourceMatchers } from '../config.mts';
 import { hasStagedFiles, stageBaseline, stagedSet } from './git-index.mts';
+import { LINES_BASELINE, SIZE_SKIP_DIRS } from './size-policy.mts';
+import { runPreflightCli } from './size-preflight.mts';
 
 // The impl-file predicate bundle sourceMatchers() returns (isSource/isTest/isBarrel).
 type SourceMatchers = ReturnType<typeof sourceMatchers>;
@@ -40,8 +42,7 @@ interface DisableCount {
   file: number; // `eslint-disable max-lines` directives in the file
   fn: number; // `eslint-disable max-lines-per-function` directives
 }
-// Per-file disable baseline so only staged-file shrink auto-lowers during a commit.
-// A pre-per-file `{ fileDisables, fnDisables }` baseline (no `files` key) is treated as NO
+// Per-file disable baseline; a pre-per-file `{ fileDisables, fnDisables }` baseline (no `files` key) is NO
 // grandfathered debt and self-deleted on the next commit; the owner re-freezes once
 // (`guard-size freeze`, or `devkit upgrade`) to re-grandfather any real disables. Baselines are
 // regenerable state, so no dual-format gate is carried.
@@ -57,8 +58,6 @@ interface LinesBaseline {
 }
 
 const BASELINE = 'eslint/baselines/size.json';
-const LINES_BASELINE = 'eslint/baselines/size-lines.json';
-const SKIP_DIRS = new Set(['node_modules', 'dist', 'out', '__snapshots__', '_shared']);
 // Only an actual directive comment counts — a line that merely MENTIONS the phrase
 // (string literal, prose comment) must not inflate the ratchet and falsely block.
 const DIRECTIVE_START = /^\s*(?:\/\/|\/\*)\s*eslint-disable/;
@@ -82,7 +81,7 @@ function walk(
   for (const e of entries) {
     const rel = `${dir}/${e.name}`;
     if (e.isDirectory()) {
-      if (!SKIP_DIRS.has(e.name)) walk(root, rel, files, match, includeTests);
+      if (!SIZE_SKIP_DIRS.has(e.name)) walk(root, rel, files, match, includeTests);
     } else if (match.isSource(e.name) && (includeTests || !match.isTest(e.name))) {
       files.push(rel);
     }
@@ -488,11 +487,12 @@ function runCli(cmd: string): void {
     process.exit(0);
   }
 
-  console.error('usage: guard-size <freeze|gate>');
+  console.error('usage: guard-size <freeze|gate|preflight --base <ref> [-- path...]>');
   process.exit(2);
 }
 
 // Run as a CLI only when invoked directly; importing this module (tests) has no side effects.
 if (process.argv[1] && import.meta.url === pathToFileURL(realpathSync(process.argv[1])).href) {
+  if (process.argv[2] === 'preflight') runPreflightCli(process.argv.slice(3));
   runCli(process.argv[2]);
 }
diff --git a/gate-engine/ratchets/size-policy.mts b/gate-engine/ratchets/size-policy.mts
new file mode 100644
index 00000000..8f71600f
--- /dev/null
+++ b/gate-engine/ratchets/size-policy.mts
@@ -0,0 +1,2 @@
+export const LINES_BASELINE = 'eslint/baselines/size-lines.json';
+export const SIZE_SKIP_DIRS = new Set(['node_modules', 'dist', 'out', '__snapshots__', '_shared']);
diff --git a/gate-engine/ratchets/size-preflight.mts b/gate-engine/ratchets/size-preflight.mts
new file mode 100644
index 00000000..a1b4dbac
--- /dev/null
+++ b/gate-engine/ratchets/size-preflight.mts
@@ -0,0 +1,146 @@
+import { execFileSync } from 'node:child_process';
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { resolveGuardConfig, sourceMatchers } from '../config.mts';
+import { stagedSet } from './git-index.mts';
+import { LINES_BASELINE, SIZE_SKIP_DIRS } from './size-policy.mts';
+
+interface LinesBaseline {
+  files: Record<string, number>;
+}
+
+interface LinesPreflightRow {
+  file: string;
+  lines: number;
+  ceiling: number;
+  headroom: number;
+  localCeiling: number;
+}
+
+function readLinesBaseline(file: string): LinesBaseline {
+  if (!existsSync(file)) return { files: {} };
+  const parsed = JSON.parse(readFileSync(file, 'utf8')) as Partial<LinesBaseline>;
+  return { files: parsed.files ?? {} };
+}
+
+function readLinesBaselineAtRef(root: string, ref: string): LinesBaseline | null {
+  execFileSync('git', ['rev-parse', '--verify', `${ref}^{commit}`], {
+    cwd: root,
+    stdio: ['ignore', 'pipe', 'ignore'],
+  });
+  const prefix = execFileSync('git', ['rev-parse', '--show-prefix'], {
+    cwd: root,
+    encoding: 'utf8',
+  }).trim();
+  let text: string;
+  try {
+    text = execFileSync('git', ['show', `${ref}:${prefix}${LINES_BASELINE}`], {
+      cwd: root,
+      encoding: 'utf8',
+      stdio: ['ignore', 'pipe', 'ignore'],
+    });
+  } catch {
+    return null;
+  }
+  const parsed = JSON.parse(text) as Partial<LinesBaseline>;
+  return { files: parsed.files ?? {} };
+}
+
+function sourcePaths(
+  root: string,
+  cfg: ReturnType<typeof resolveGuardConfig>,
+  selected: string[],
+): string[] {
+  const match = sourceMatchers(cfg.sourceExtensions);
+  return selected.filter(
+    (file) =>
+      existsSync(join(root, file)) &&
+      match.isSource(file) &&
+      !file.split('/').some((part) => SIZE_SKIP_DIRS.has(part)) &&
+      cfg.scanRoots.some(
+        (scanRoot: string) => file === scanRoot || file.startsWith(`${scanRoot}/`),
+      ),
+  );
+}
+
+// Compare the caller's current bytes with the raw-line baseline from the exact ref a ship will use.
+// A missing ref baseline is an overlay/untracked baseline, which ship links from the working copy.
+export function preflightLines(root: string, ref: string, requested: string[] = []): number {
+  let cfg: ReturnType<typeof resolveGuardConfig>;
+  let local: LinesBaseline;
+  try {
+    cfg = resolveGuardConfig(root);
+    if (!cfg.maxLines && !cfg.maxTestLines) return 0;
+    local = readLinesBaseline(join(root, LINES_BASELINE));
+  } catch (error) {
+    console.error(`guard-size preflight unavailable: ${String(error)}`);
+    return 2;
+  }
+  let committed: LinesBaseline | null;
+  try {
+    committed = readLinesBaselineAtRef(root, ref);
+  } catch (error) {
+    console.error(`guard-size preflight unavailable at ${ref}: ${String(error)}`);
+    return 2;
+  }
+  const match = sourceMatchers(cfg.sourceExtensions);
+  const cap = (file: string) => (match.isTest(file) ? cfg.maxTestLines : cfg.maxLines);
+  const selected = requested.length > 0 ? requested : [...(stagedSet(root) ?? [])];
+  const baselineIncluded = selected.includes(LINES_BASELINE);
+  const files = sourcePaths(root, cfg, selected).filter((file) => cap(file) > 0);
+  if (files.length === 0) {
+    if (requested.length === 0) {
+      console.error('guard-size preflight: no staged source files (pass paths after `--`).');
+      return 2;
+    }
+    console.log(`guard-size preflight: no source files in scope: ${requested.join(', ')}`);
+    return 0;
+  }
+
+  const usesWorkingBaseline = baselineIncluded || !committed;
+  const baseline: LinesBaseline = usesWorkingBaseline ? local : (committed ?? local);
+  const baselineLabel = usesWorkingBaseline ? 'working tree' : ref;
+  let rows: LinesPreflightRow[];
+  try {
+    rows = files.map((file) => {
+      const lines = readFileSync(join(root, file), 'utf8').split('\n').length;
+      const ceiling = Math.max(cap(file), baseline.files[file] ?? 0);
+      const localCeiling = Math.max(cap(file), local.files[file] ?? 0);
+      return { file, lines, ceiling, headroom: ceiling - lines, localCeiling };
+    });
+  } catch (error) {
+    console.error(`guard-size preflight unavailable while reading source files: ${String(error)}`);
+    return 2;
+  }
+
+  console.log(`guard-size preflight — effective ceilings from ${baselineLabel}`);
+  for (const row of rows) {
+    const drift =
+      committed && row.localCeiling !== row.ceiling
+        ? `; working-tree max ${row.localCeiling} differs by ${row.localCeiling - row.ceiling}`
+        : '';
+    console.log(
+      `   ${row.file}: ${row.lines} lines; max ${row.ceiling}; headroom ${row.headroom}${drift}`,
+    );
+  }
+
+  const grew = rows.filter((row) => row.headroom < 0);
+  if (grew.length === 0) return 0;
+  console.error(`🚫 ${grew.length} file(s) exceed the line limit from ${baselineLabel}:`);
+  for (const row of grew) {
+    const drift =
+      committed && row.localCeiling !== row.ceiling
+        ? `; working-tree baseline would allow ${row.localCeiling}`
+        : '';
+    console.error(`   ${row.file}: ${row.lines} lines (max ${row.ceiling}${drift})`);
+  }
+  return 1;
+}
+
+export function runPreflightCli(args: string[]): never {
+  if (args[0] !== '--base' || !args[1] || (args.length > 2 && args[2] !== '--')) {
+    console.error('usage: guard-size preflight --base <ref> [-- path...]');
+    process.exit(2);
+  }
+  process.exit(preflightLines(process.cwd(), args[1], args.slice(3)));
+}
diff --git a/skills/using-devkit/SKILL.md b/skills/using-devkit/SKILL.md
index 304e3da4..7e428617 100644
--- a/skills/using-devkit/SKILL.md
+++ b/skills/using-devkit/SKILL.md
@@ -37,6 +37,7 @@ devkit command.
 | You observe (trigger) | Run | Why not the raw-git move |
 |---|---|---|
 | A commit was **denied on a protected branch**, or you're on `main`/`master` and need to land a change | `devkit ship <branch> "<title>" -- <paths>` | `git switch -c` + commit + push **moves the shared checkout's HEAD**, disturbing parallel agents; `ship` commits in an ephemeral worktree and opens a PR without moving HEAD |
+| You need to preview a hot file's real line ceiling before shipping | `guard-size preflight --base origin/<branch> -- <paths>` | It reads `size-lines.json` from the requested base, prints current lines / effective cap / headroom, and names any stale working-tree baseline. `devkit ship` runs the same preflight automatically before creating its gate worktree. |
 | The PR must target a branch **other than the one you're on** — e.g. your work is already committed on a source branch and the base is a different one | `devkit ship <branch> "<title>" --base <base-branch> -- <paths>` (branch + title FIRST — see Rules) | plain `ship` bases on this checkout's HEAD, where those paths are already identical, so it stages nothing and aborts `nothing to commit`; `--base` diffs your **working tree** against `origin/<base-branch>` and targets the PR there — no checkout, no worktree juggling |
 | You're in a **linked worktree, already on a branch**, and need a PR | `devkit ship <new-branch> "<title>" --base <base> -- <paths>` | you don't need — and must not create — another branch: `ship` makes the PR branch itself, and a branch that already exists is the one state it cannot recover from |
 | Ship reports the branch **already exists on origin** (an open PR uses it) | `devkit ship <branch> "<title>" --pr -- <paths>` | picking a new name orphans the existing PR; `--pr` fast-forwards a new commit onto that branch instead |