test: strengthen evidence runtime handoff coverage

backend/test/workspace-runtime-handoff.test.ts

@@ -141,7 +141,7 @@ async function fixture(workspaceSource = filesystemWorkspace) {
   };
   for (const [name, value] of Object.entries(environment)) vi.stubEnv(name, value);
   vi.stubEnv("THT_HOME", join(root, "home"));
-  return { root, dataRoot, secretRoot, registry, registryConfig, revision };
+  return { root, source, dataRoot, secretRoot, registry, registryConfig, revision };
 }
 
 function runnerFor(f: Awaited<ReturnType<typeof fixture>>): ThtRunner {
@@ -234,6 +234,52 @@ test("separate runtime leases hand off byte-identical revision Evidence configs
   }
 });
 
+test("real Evidence-content-only commit changes runtime identity and root with identical descriptor YAML", async () => {
+  const f = await fixture();
+  const runner = runnerFor(f);
+  const first = runner.acquireWorkspaceRuntime(f.revision.snapshotPath);
+  const descriptorBefore = readFileSync(f.revision.snapshotPath, "utf8");
+  writeFileSync(
+    join(f.source, "workspace-content", "psd-clinical", "evidence", "guide.md"),
+    "# Content-only revision two\n",
+  );
+  await git(f.source, ["add", "workspace-content/psd-clinical/evidence/guide.md"]);
+  await git(f.source, ["commit", "-m", "Update Evidence content only"]);
+  await git(f.source, ["push", "origin", "main"]);
+  await f.registry.pull();
+  const current = (await f.registry.list())[0];
+  const second = runner.acquireWorkspaceRuntime(current.snapshotPath);
+
+  try {
+    expect(current.commit).not.toBe(f.revision.commit);
+    expect(current.blob).toBe(f.revision.blob);
+    expect(readFileSync(current.snapshotPath, "utf8")).toBe(descriptorBefore);
+    const firstRendered = parse(readFileSync(first.path, "utf8"));
+    const secondRendered = parse(readFileSync(second.path, "utf8"));
+    expect(firstRendered.runtime_identity.workspace_revision).toBe(f.revision.commit);
+    expect(secondRendered.runtime_identity.workspace_revision).toBe(current.commit);
+    expect(secondRendered.evidence.sources[0].root).toBe(join(
+      f.registryConfig.root,
+      "snapshots",
+      current.commit,
+      "workspace-content",
+      "psd-clinical",
+      "evidence",
+    ));
+    expect(secondRendered.evidence.sources[0].root).not.toBe(firstRendered.evidence.sources[0].root);
+
+    for (const lease of [first, second]) {
+      await expect(runFile(thtBin, ["config", "check", "-c", lease.path], {
+        cwd: harnessDir,
+        env: { ...process.env, THT_HOME: join(f.root, "home") },
+      })).resolves.toBeDefined();
+    }
+  } finally {
+    first.release();
+    second.release();
+  }
+});
+
 test("signed HTTP Evidence resolves its file binding and config check never captures its contents", async () => {
   const f = await fixture(evidenceWorkspace(`    type: http
     uris: [https://evidence.example.test/guide.md]