diff --git a/scripts/migrations/337-claude-sonnet-5-additive.js b/scripts/migrations/337-claude-sonnet-5-additive.js
index d02b6d03af..92306e3d1c 100644
--- a/scripts/migrations/337-claude-sonnet-5-additive.js
+++ b/scripts/migrations/337-claude-sonnet-5-additive.js
@@ -10,9 +10,10 @@
  * that record: the reviewer/task model pickers reading it offer the retired
  * sonnet and cannot offer the current one at all.
  *
- * ADDITIVE, deliberately — the opposite policy from 153/206 and from
- * `makeSeededProviderTierMigration`, because this one runs against lists the
- * user curated:
+ * Built on `makeAdditiveProviderInsertMigration` (`_lib.js` family 7b) —
+ * ADDITIVE, deliberately the opposite policy from 153/206 and from
+ * `makeSeededProviderTierMigration` (family 7), because this one runs against
+ * lists the user curated:
  *
  *   - `claude-sonnet-5` is INSERTED right after `claude-sonnet-4-6`, and the
  *     retired id is KEPT. `claude-sonnet-4-6` still resolves for the CLI, so
@@ -27,56 +28,16 @@
  * or a fresh `data.reference` seed already put it there) and on a second run.
  */
 
-import { readProvidersDoc, writeJsonAtomic } from './_lib.js';
-
-const PROVIDERS_REL_PATH = 'data/providers.json';
+import { makeAdditiveProviderInsertMigration } from './_lib.js';
 
 // The four seeded Claude records and the sonnet id each one spells. The Bedrock
 // pair uses the region-qualified form its own environment resolves — inserting a
 // bare `claude-sonnet-5` there would offer an id that record cannot run.
-const TARGETS = [
+export const TARGETS = [
   { id: 'claude-code', retired: 'claude-sonnet-4-6', current: 'claude-sonnet-5' },
   { id: 'claude-code-tui', retired: 'claude-sonnet-4-6', current: 'claude-sonnet-5' },
   { id: 'claude-code-bedrock', retired: 'us.anthropic.claude-sonnet-4-6', current: 'us.anthropic.claude-sonnet-5' },
   { id: 'claude-code-tui-bedrock', retired: 'us.anthropic.claude-sonnet-4-6', current: 'us.anthropic.claude-sonnet-5' },
 ];
 
-export default {
-  async up({ rootDir }) {
-    const doc = await readProvidersDoc({ rootDir });
-    if (!doc.ok) {
-      if (doc.reason === 'no-file') console.log(`📄 ${PROVIDERS_REL_PATH} not present — skipping (fresh install seeds claude-sonnet-5 from data.reference)`);
-      else if (doc.reason === 'unreadable') console.log(`⚠️ ${PROVIDERS_REL_PATH}: invalid JSON, skipping (${doc.err.message})`);
-      else console.log(`⚠️ ${PROVIDERS_REL_PATH}: unexpected shape, skipping`);
-      return { ok: false, reason: doc.reason, updated: 0 };
-    }
-
-    const { config, providers, path: providersPath } = doc;
-    const touched = [];
-
-    for (const { id, retired, current } of TARGETS) {
-      const provider = providers[id];
-      if (!provider || !Array.isArray(provider.models)) continue;
-      const at = provider.models.indexOf(retired);
-      // Nothing to repair unless the retired id is listed AND the current one
-      // isn't: an already-current record (seeded, or bumped by 153) is a no-op,
-      // and a record that never listed the retired tier is not this bug.
-      if (at === -1 || provider.models.includes(current)) continue;
-      provider.models = [
-        ...provider.models.slice(0, at + 1),
-        current,
-        ...provider.models.slice(at + 1),
-      ];
-      touched.push(id);
-    }
-
-    if (touched.length === 0) {
-      console.log(`✅ ${PROVIDERS_REL_PATH}: Claude sonnet tier already current — no change`);
-      return { ok: true, reason: 'already-current', updated: 0 };
-    }
-
-    await writeJsonAtomic(providersPath, config);
-    console.log(`📝 ${PROVIDERS_REL_PATH}: offered claude-sonnet-5 on ${touched.join(', ')}`);
-    return { ok: true, reason: 'updated', updated: touched.length };
-  },
-};
+export default makeAdditiveProviderInsertMigration({ targets: TARGETS, label: 'claude-sonnet-5' });
diff --git a/scripts/migrations/337-claude-sonnet-5-additive.test.js b/scripts/migrations/337-claude-sonnet-5-additive.test.js
index 47316977fe..f9503aabe0 100644
--- a/scripts/migrations/337-claude-sonnet-5-additive.test.js
+++ b/scripts/migrations/337-claude-sonnet-5-additive.test.js
@@ -1,125 +1,14 @@
 /**
  * Test for migration 337 — offer `claude-sonnet-5` on a Claude CLI/TUI record
- * that still lists only the retired `claude-sonnet-4-6` tier.
+ * that still lists only the retired `claude-sonnet-4-6` tier. Built on
+ * `makeAdditiveProviderInsertMigration` (`_lib.js` family 7b); the shared
+ * contract lives in `runAdditiveProviderInsertMigrationTests`
+ * (`_testHelpers.js`) and is exercised here against 337's own `targets`.
  */
-import { describe, it, expect, beforeEach, afterEach } from 'vitest';
-import { mkdtempSync, rmSync, writeFileSync, readFileSync, mkdirSync } from 'fs';
-import { tmpdir } from 'os';
-import { join } from 'path';
-
-import migration from './337-claude-sonnet-5-additive.js';
-
-const writeJson = (path, value) => writeFileSync(path, JSON.stringify(value, null, 2) + '\n');
-const readJson = (path) => JSON.parse(readFileSync(path, 'utf-8'));
+import { describe } from 'vitest';
+import migration, { TARGETS } from './337-claude-sonnet-5-additive.js';
+import { runAdditiveProviderInsertMigrationTests } from './_testHelpers.js';
 
 describe('migration 337 — claude-sonnet-5 additive repair', () => {
-  let rootDir;
-  let providersPath;
-
-  beforeEach(() => {
-    rootDir = mkdtempSync(join(tmpdir(), 'portos-337-'));
-    mkdirSync(join(rootDir, 'data'));
-    providersPath = join(rootDir, 'data', 'providers.json');
-  });
-
-  afterEach(() => rmSync(rootDir, { recursive: true, force: true }));
-
-  const seed = (providers) => writeJson(providersPath, { activeProvider: 'claude-code', providers });
-
-  it('inserts claude-sonnet-5 after the retired tier on a CURATED list 153 skipped', async () => {
-    seed({
-      'claude-code': {
-        models: ['claude-haiku-4-5', 'claude-sonnet-4-6', 'claude-opus-5', 'claude-fable-5'],
-        defaultModel: 'claude-opus-5',
-        mediumModel: 'claude-sonnet-4-6',
-      },
-    });
-
-    const result = await migration.up({ rootDir });
-
-    expect(result).toMatchObject({ ok: true, reason: 'updated', updated: 1 });
-    const after = readJson(providersPath).providers['claude-code'];
-    expect(after.models).toEqual([
-      'claude-haiku-4-5', 'claude-sonnet-4-6', 'claude-sonnet-5', 'claude-opus-5', 'claude-fable-5',
-    ]);
-    // Additive: the retired id and every tier pointer survive untouched.
-    expect(after.mediumModel).toBe('claude-sonnet-4-6');
-    expect(after.defaultModel).toBe('claude-opus-5');
-  });
-
-  it('uses each Bedrock record\'s own region-qualified sonnet spelling', async () => {
-    seed({
-      'claude-code-bedrock': {
-        models: ['us.anthropic.claude-haiku-4-5', 'us.anthropic.claude-sonnet-4-6', 'global.anthropic.claude-opus-5'],
-      },
-      'claude-code-tui-bedrock': {
-        models: ['us.anthropic.claude-sonnet-4-6'],
-      },
-    });
-
-    const result = await migration.up({ rootDir });
-
-    expect(result.updated).toBe(2);
-    const { providers } = readJson(providersPath);
-    expect(providers['claude-code-bedrock'].models).toEqual([
-      'us.anthropic.claude-haiku-4-5',
-      'us.anthropic.claude-sonnet-4-6',
-      'us.anthropic.claude-sonnet-5',
-      'global.anthropic.claude-opus-5',
-    ]);
-    expect(providers['claude-code-tui-bedrock'].models).toEqual([
-      'us.anthropic.claude-sonnet-4-6',
-      'us.anthropic.claude-sonnet-5',
-    ]);
-    // The bare id must never leak into a Bedrock record — its environment
-    // resolves only the region-qualified form.
-    expect(providers['claude-code-bedrock'].models).not.toContain('claude-sonnet-5');
-  });
-
-  it('is a no-op on an already-current record and on a second run', async () => {
-    seed({
-      'claude-code': { models: ['claude-haiku-4-5', 'claude-sonnet-5', 'claude-opus-5'] },
-      'claude-code-tui': { models: ['claude-haiku-4-5', 'claude-sonnet-4-6', 'claude-sonnet-5'] },
-    });
-
-    const first = await migration.up({ rootDir });
-    expect(first).toMatchObject({ ok: true, reason: 'already-current', updated: 0 });
-
-    // And a record it DID repair stays repaired rather than gaining a duplicate.
-    seed({ 'claude-code': { models: ['claude-sonnet-4-6'] } });
-    expect((await migration.up({ rootDir })).updated).toBe(1);
-    const second = await migration.up({ rootDir });
-    expect(second.updated).toBe(0);
-    expect(readJson(providersPath).providers['claude-code'].models)
-      .toEqual(['claude-sonnet-4-6', 'claude-sonnet-5']);
-  });
-
-  it('leaves records outside the four seeded Claude ids alone', async () => {
-    seed({
-      'claude-ollama': { models: ['claude-sonnet-4-6'] },
-      'antigravity-cli': { models: ['claude-sonnet-4-6'] },
-    });
-
-    expect((await migration.up({ rootDir })).updated).toBe(0);
-    const { providers } = readJson(providersPath);
-    expect(providers['claude-ollama'].models).toEqual(['claude-sonnet-4-6']);
-    expect(providers['antigravity-cli'].models).toEqual(['claude-sonnet-4-6']);
-  });
-
-  it('skips a missing or malformed providers file without throwing', async () => {
-    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'no-file' });
-
-    writeFileSync(providersPath, '{not json');
-    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'unreadable' });
-
-    writeJson(providersPath, { activeProvider: 'claude-code' });
-    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'bad-shape' });
-  });
-
-  it('skips a record whose models field is not an array', async () => {
-    seed({ 'claude-code': { models: 'claude-sonnet-4-6', defaultModel: 'claude-sonnet-4-6' } });
-
-    expect((await migration.up({ rootDir })).updated).toBe(0);
-    expect(readJson(providersPath).providers['claude-code'].models).toBe('claude-sonnet-4-6');
-  });
+  runAdditiveProviderInsertMigrationTests({ migration, targets: TARGETS, prefix: 'migration-337-' });
 });
diff --git a/scripts/migrations/_lib.js b/scripts/migrations/_lib.js
index 1405d5c5a0..a0df499dbf 100644
--- a/scripts/migrations/_lib.js
+++ b/scripts/migrations/_lib.js
@@ -22,11 +22,22 @@
  *      032 / 058 / 153 / 206 each hand-copied. Those four stay frozen; the
  *      factory is for the next RETIREMENT bump. It expresses id→id retirement
  *      only: `idMap` maps 1:1 over `oldModels`, and `swapTierPointers` moves
- *      EVERY pointer off a retired id. An ADDITIVE change — appending a model
- *      while keeping the old one listed, or re-pointing some tiers but not all
- *      (292, 294) — does not fit, and hand-rolls on `readProvidersDoc` instead.
+ *      EVERY pointer off a retired id. This is a **pristine-list rewrite** —
+ *      only an EXACT match of the prior seeded `models` array qualifies, so a
+ *      curated list is left alone rather than reset.
+ *   7b. Additive provider-model inserts — `makeAdditiveProviderInsertMigration`
+ *       (337 is the first and, so far, only member) is the opposite policy for
+ *       the SAME `data/providers.json` targets: it runs against a list the user
+ *       may have curated, so it never rewrites or drops anything — it only
+ *       splices `current` in immediately after `retired` when `retired` is
+ *       listed and `current` is not, regardless of what else the list holds.
+ *       Tier pointers are left alone (a curated list is exactly where
+ *       re-pointing would override a deliberate choice). Reach for family 7
+ *       when retiring an id from the shipped seed; reach for 7b when a later
+ *       tier needs to be OFFERED without disturbing whatever the user already
+ *       has listed.
  *
- * Families 5 and 7 both target `data/providers.json` and share its
+ * Families 5, 7, and 7b all target `data/providers.json` and share its
  * read → parse → shape-guard preamble via `readProvidersDoc`; each still owns
  * its own log copy and result shape.
  *
@@ -1080,6 +1091,84 @@ export function makeSeededProviderTierMigration({ targets, tierLabel }) {
   return { up };
 }
 
+// ---- additive provider-model insert migration family (7b) ----
+//
+// The opposite policy from family 7, for the same `data/providers.json`
+// targets: family 7 rewrites a PRISTINE seeded list wholesale; this one splices
+// a new id into a list the user may have curated, touching nothing else.
+// 337 is the first member and the shell every future "offer a model without
+// disturbing what's already listed" migration should reach for instead of
+// hand-copying it a fourth time.
+
+/**
+ * Build an additive provider-model insert migration's `up()`. Returns `{ up }`,
+ * so a migration collapses to
+ * `export default makeAdditiveProviderInsertMigration({ targets, label })`
+ * over a small data table.
+ *
+ *   - `targets` — `[{ id, retired, current }, …]`, one entry per provider
+ *     record this migration can touch. `retired` and `current` are per-target
+ *     (not shared across the table) so sibling records that spell the same
+ *     tier differently — e.g. a Bedrock record's region-qualified id versus the
+ *     bare CLI id — each get their own exact strings; inserting one target's
+ *     `current` onto another target's record would offer an id that record's
+ *     environment cannot resolve.
+ *   - `label` — the human name of the tier being offered, used in the log
+ *     copy (`"offered ${label} on …"`, `"${label} already current"`).
+ *
+ * For each target: if `retired` is listed in the record's `models` and
+ * `current` is not, `current` is spliced in immediately after `retired` —
+ * `retired` itself, every other entry, and every tier pointer are left
+ * exactly as found. A record already listing `current`, or never listing
+ * `retired`, is untouched — which makes a second run, and a fresh install
+ * already seeded with `current`, both no-ops.
+ *
+ * Resolves to `{ ok, reason: 'no-file' | 'unreadable' | 'bad-shape' |
+ * 'already-current' | 'updated', updated }`.
+ */
+export function makeAdditiveProviderInsertMigration({ targets, label }) {
+  async function up({ rootDir }) {
+    const doc = await readProvidersDoc({ rootDir });
+    if (!doc.ok) {
+      if (doc.reason === 'no-file') console.log(`📄 ${PROVIDERS_REL_PATH} not present — skipping (fresh install seeds ${label} from data.reference)`);
+      else if (doc.reason === 'unreadable') console.log(`⚠️ ${PROVIDERS_REL_PATH}: invalid JSON, skipping (${doc.err.message})`);
+      else console.log(`⚠️ ${PROVIDERS_REL_PATH}: unexpected shape, skipping`);
+      return { ok: false, reason: doc.reason, updated: 0 };
+    }
+
+    const { config, providers, path: providersPath } = doc;
+    const touched = [];
+
+    for (const { id, retired, current } of targets) {
+      const provider = providers[id];
+      if (!provider || !Array.isArray(provider.models)) continue;
+      const at = provider.models.indexOf(retired);
+      // Nothing to repair unless the retired id is listed AND the current one
+      // isn't: an already-current record (seeded, or bumped by a prior run) is
+      // a no-op, and a record that never listed the retired tier is not this
+      // migration's concern.
+      if (at === -1 || provider.models.includes(current)) continue;
+      provider.models = [
+        ...provider.models.slice(0, at + 1),
+        current,
+        ...provider.models.slice(at + 1),
+      ];
+      touched.push(id);
+    }
+
+    if (touched.length === 0) {
+      console.log(`✅ ${PROVIDERS_REL_PATH}: ${label} already current — no change`);
+      return { ok: true, reason: 'already-current', updated: 0 };
+    }
+
+    await writeJsonAtomic(providersPath, config);
+    console.log(`📝 ${PROVIDERS_REL_PATH}: offered ${label} on ${touched.join(', ')}`);
+    return { ok: true, reason: 'updated', updated: touched.length };
+  }
+
+  return { up };
+}
+
 /**
  * Build the per-subdir prompt-drift tables that `scripts/setup-data.js` uses
  * for its "pending migration" warning by sweeping every numbered migration's
diff --git a/scripts/migrations/_testHelpers.js b/scripts/migrations/_testHelpers.js
index 8fd1dbff98..cc75d1fcec 100644
--- a/scripts/migrations/_testHelpers.js
+++ b/scripts/migrations/_testHelpers.js
@@ -10,6 +10,10 @@
  *     with `makeSeededProviderTierMigration`. Every fixture is derived from the
  *     migration's own `targets` table, so a bump's test is a `describe` + one
  *     call and still asserts the full conservative contract.
+ *   - `runAdditiveProviderInsertMigrationTests` — additive provider-model
+ *     inserts built with `makeAdditiveProviderInsertMigration` (family 7b).
+ *     Same shape: a `describe` + one call, with fixtures derived from the
+ *     migration's own `targets` array.
  */
 
 import { it, expect, beforeEach, afterEach } from 'vitest';
@@ -378,3 +382,128 @@ export function runSeededProviderTierMigrationTests({ migration, targets, prefix
     }
   });
 }
+
+// ---- additive provider-model insert migrations (family 7b) ----
+
+/**
+ * Standard suite for a migration built with `makeAdditiveProviderInsertMigration`.
+ * A migration's `*.test.js` collapses to a `describe` + a single
+ * `runAdditiveProviderInsertMigrationTests({ migration, targets, prefix })` call.
+ *
+ *   - `migration` — the migration's default export (`{ up }`).
+ *   - `targets`   — the SAME `targets` array passed to the factory
+ *     (`[{ id, retired, current }, …]`). Every fixture is derived from it, so
+ *     the suite covers each target the migration actually ships.
+ *   - `prefix`    — `mkdtempSync` directory name (`'migration-337-'`), so a
+ *     debugger leaves a recognizable sandbox in the temp dir.
+ */
+export function runAdditiveProviderInsertMigrationTests({ migration, targets, prefix }) {
+  let rootDir;
+  let providersPath;
+
+  beforeEach(() => {
+    rootDir = mkdtempSync(join(tmpdir(), prefix));
+    mkdirSync(join(rootDir, 'data'), { recursive: true });
+    providersPath = join(rootDir, 'data', 'providers.json');
+  });
+
+  afterEach(() => {
+    rmSync(rootDir, { recursive: true, force: true });
+  });
+
+  const write = (providers) => writeFileSync(providersPath, JSON.stringify({ providers }, null, 2) + '\n');
+  const read = () => JSON.parse(readFileSync(providersPath, 'utf-8')).providers;
+  const raw = () => readFileSync(providersPath, 'utf-8');
+
+  it('declares at least one target', () => {
+    expect(targets.length).toBeGreaterThan(0);
+    for (const { retired, current } of targets) {
+      expect(retired).not.toBe(current);
+    }
+  });
+
+  it('inserts each target\'s current id right after its retired id on a curated list, leaving pointers alone', async () => {
+    write(Object.fromEntries(targets.map(({ id, retired }) => [
+      id,
+      { models: ['unrelated-tier', retired, 'sibling-tier'], defaultModel: 'unrelated-tier', mediumModel: retired },
+    ])));
+
+    const result = await migration.up({ rootDir });
+
+    expect(result).toMatchObject({ ok: true, reason: 'updated', updated: targets.length });
+    const out = read();
+    for (const { id, retired, current } of targets) {
+      expect(out[id].models).toEqual(['unrelated-tier', retired, current, 'sibling-tier']);
+      // Additive: the retired id and every tier pointer survive untouched.
+      expect(out[id].defaultModel).toBe('unrelated-tier');
+      expect(out[id].mediumModel).toBe(retired);
+    }
+  });
+
+  it('never offers one target\'s current id on a different target\'s record', async () => {
+    const distinct = targets.filter(({ current }, i) => targets.findIndex((t) => t.current === current) === i);
+    if (distinct.length < 2) return; // nothing to cross-check when every target shares one id
+    write(Object.fromEntries(targets.map(({ id, retired }) => [id, { models: [retired] }])));
+
+    await migration.up({ rootDir });
+
+    const out = read();
+    for (const { id, current } of targets) {
+      for (const other of distinct) {
+        if (other.current === current) continue;
+        expect(out[id].models).not.toContain(other.current);
+      }
+    }
+  });
+
+  it('is a no-op on an already-current record and on a second run', async () => {
+    const [first, ...rest] = targets;
+    write(Object.fromEntries([
+      [first.id, { models: [first.retired, first.current] }],
+      ...rest.map(({ id, retired }) => [id, { models: [retired] }]),
+    ]));
+
+    const before = raw();
+    const firstRun = await migration.up({ rootDir });
+    expect(firstRun.updated).toBe(rest.length);
+    if (rest.length > 0) expect(raw()).not.toBe(before); // the repairable targets did get written once
+
+    // A record repaired on the first run is untouched by a second — no
+    // duplicate insert — and the already-current record was never touched.
+    const secondRun = await migration.up({ rootDir });
+    expect(secondRun).toMatchObject({ ok: true, reason: 'already-current', updated: 0 });
+    for (const { id, retired, current } of targets) {
+      expect(read()[id].models).toEqual([retired, current]);
+    }
+  });
+
+  it('leaves providers outside the target set untouched', async () => {
+    const unrelated = { id: 'unrelated-provider', models: ['some-configured-default'], defaultModel: 'some-configured-default' };
+    write({
+      ...Object.fromEntries(targets.map(({ id, retired }) => [id, { models: [retired] }])),
+      'unrelated-provider': unrelated,
+    });
+
+    await migration.up({ rootDir });
+
+    expect(read()['unrelated-provider']).toEqual(unrelated);
+  });
+
+  it('skips a missing or malformed providers file without throwing', async () => {
+    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'no-file' });
+
+    writeFileSync(providersPath, '{not json');
+    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'unreadable' });
+
+    writeFileSync(providersPath, JSON.stringify({ activeProvider: 'x' }, null, 2) + '\n');
+    expect(await migration.up({ rootDir })).toMatchObject({ ok: false, reason: 'bad-shape' });
+  });
+
+  it('skips a record whose models field is not an array', async () => {
+    const [first] = targets;
+    write({ [first.id]: { models: first.retired, defaultModel: first.retired } });
+
+    expect((await migration.up({ rootDir })).updated).toBe(0);
+    expect(read()[first.id].models).toBe(first.retired);
+  });
+}