FN-7486: fix no-diff merge recovery ownership checks

Fix no-op task branch recovery by recognizing canonical branches with no unique diff before rejecting inherited foreign trailers.

- Add no-diff ownership classification for already-merged detection when canonical task branches inherit another task's landed commit.
- Teach self-healing and branch-misbound recovery to ignore foreign branch-tip trailers only for branches proven to have no unique task diff.
- Skip synthetic verify:fast typechecks for JavaScript alias packages without tsconfig files and cover the behavior with tests.
- Add regression coverage and a patch changeset for the recovery fix.

Files changed:
 .changeset/fn-7486-merge-recovery-noop-ownership.md       |  7 ++
 .../already-merged-detector.real-git.test.ts       | 68 +++++++++++++++++
 .../self-healing-already-merged.real-git.test.ts   | 89 ++++++++++++++++++++--
 packages/engine/src/already-merged-detector.ts     | 88 +++++++++++++++------
 packages/engine/src/self-healing.ts                | 61 +++++++++++++--
 scripts/__tests__/verify-fast.test.mjs             | 16 +++-
 scripts/verify-fast.mjs                            | 15 +++-
 7 files changed, 303 insertions(+), 41 deletions(-)

Fusion-Task-Id: FN-7486

Fusion-Task-Lineage: 4185c6ed-9731-4ffc-b033-34bf0c3a83ad

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

scripts/__tests__/verify-fast.test.mjs

@@ -110,7 +110,7 @@ test("buildVerifyPlan: typecheck for all eligible, then builds, then boot smoke
 test("buildVerifyPlan: a package without a build script gets a typecheck step but no build step", () => {
   const packageMeta = new Map([
     ["@fusion/engine", { hasTypecheck: true, hasBuild: true }],
-    ["@fusion/test-only", { hasTypecheck: false, hasBuild: false }],
+    ["@fusion/test-only", { hasTypecheck: false, hasTsconfig: true, hasBuild: false }],
   ]);
   const plan = buildVerifyPlan({ packages: ["@fusion/engine", "@fusion/test-only"], packageMeta, bootSmokeScriptPath: SMOKE, nodeBin: NODE });
   assert.deepEqual(stepIds(plan), [
@@ -126,6 +126,20 @@ test("buildVerifyPlan: a package without a build script gets a typecheck step bu
   assert.deepEqual(tc.args, ["--filter", "@fusion/test-only", "exec", "tsc", "--noEmit", "-p", "."]);
 });
 
+test("buildVerifyPlan: skips synthetic typecheck for JavaScript alias packages with no tsconfig", () => {
+  const packageMeta = new Map([
+    ["runfusion.ai", { hasTypecheck: false, hasTsconfig: false, hasBuild: false }],
+    ["@runfusion/fusion", { hasTypecheck: true, hasTsconfig: true, hasBuild: true }],
+  ]);
+  const plan = buildVerifyPlan({ packages: ["runfusion.ai", "@runfusion/fusion"], packageMeta, bootSmokeScriptPath: SMOKE, nodeBin: NODE });
+  assert.deepEqual(stepIds(plan), [
+    "bootstrap-artifacts",
+    "typecheck:@runfusion/fusion",
+    "build:@runfusion/fusion",
+    "boot-smoke",
+  ]);
+});
+
 test("buildVerifyPlan: desktop/mobile are excluded from scoped steps but boot smoke still runs", () => {
   const packageMeta = new Map([
     ["@fusion/engine", { hasTypecheck: true, hasBuild: true }],

scripts/verify-fast.mjs

@@ -32,7 +32,7 @@ of blocking forever, and we exit nonzero on the first failing step.
 */
 
 import path from "node:path";
-import { readFileSync } from "node:fs";
+import { existsSync, readFileSync } from "node:fs";
 import { spawn } from "node:child_process";
 import { fileURLToPath } from "node:url";
 
@@ -135,7 +135,7 @@ export function buildArtifactBootstrapStep(bootstrapScriptPath, nodeBin = proces
  *
  * @param {object} opts
  * @param {string[]} [opts.packages]  affected package names
- * @param {Map<string, { dir?: string, hasTypecheck?: boolean, hasBuild?: boolean }>} [opts.packageMeta]
+ * @param {Map<string, { dir?: string, hasTypecheck?: boolean, hasTsconfig?: boolean, hasBuild?: boolean }>} [opts.packageMeta]
  * @param {string} opts.bootSmokeScriptPath
  * @param {string} [opts.artifactBootstrapScriptPath]
  * @param {string} [opts.nodeBin]
@@ -147,7 +147,13 @@ export function buildVerifyPlan({ packages = [], packageMeta = new Map(), bootSm
 
   const steps = [buildArtifactBootstrapStep(bootstrapScriptPath, nodeBin)];
   for (const pkg of eligiblePackages) {
-    steps.push(buildTypecheckStep(pkg, packageMeta.get(pkg) ?? {}));
+    const meta = packageMeta.get(pkg) ?? {};
+    /*
+    FNXC:TestInfrastructure 2026-07-03-21:54:
+    Workspace alias packages such as `runfusion.ai` are publishable JavaScript shims with no tsconfig. verify:fast should not synthesize a `tsc -p .` fallback for those packages; their executable behavior is covered by the required CLI build and boot smoke.
+    */
+    if (meta.hasTypecheck === false && meta.hasTsconfig === false) continue;
+    steps.push(buildTypecheckStep(pkg, meta));
   }
 
   const builtPackages = new Set();
@@ -181,7 +187,7 @@ export function buildVerifyPlan({ packages = [], packageMeta = new Map(), bootSm
  * @param {string[]} packages
  * @param {Map<string, string>} packageDirByName  pkg name → repo-relative dir
  * @param {string} [root]
- * @returns {Map<string, { dir: string, hasTypecheck: boolean, hasBuild: boolean }>}
+ * @returns {Map<string, { dir: string, hasTypecheck: boolean, hasTsconfig: boolean, hasBuild: boolean }>}
  */
 export function readPackageMeta(packages, packageDirByName, root = repoRoot) {
   const meta = new Map();
@@ -199,6 +205,7 @@ export function readPackageMeta(packages, packageDirByName, root = repoRoot) {
     meta.set(pkg, {
       dir: dir ?? null,
       hasTypecheck: typeof scripts.typecheck === "string",
+      hasTsconfig: dir ? existsSync(path.join(root, dir, "tsconfig.json")) : true,
       hasBuild: typeof scripts.build === "string",
     });
   }