FN-6218: restore pi upgrade compatibility

Restore Pi-upgraded workspaces to keep Fusion resources accessible and recover title generation when configured models go stale.

- Mark read-only Fusion/Pi provider settings views as project-trusted so extension loading keeps working after Pi upgrades.
- Retry task title summarization with automatic model resolution when the configured provider model is missing from the Pi registry.
- Cover provider settings trust behavior and stale summarizer fallback paths with regression tests.
- Document the read-only settings trust contract and add a patch changeset.

Files changed:
 .changeset/fn-6218-pi-upgrade-regressions.md       |   5 +
 docs/settings-reference.md                         |   2 +
 docs/task-management.md                            |   2 +
 .../commands/__tests__/provider-settings.test.ts   |  16 ++++
 packages/cli/src/commands/provider-settings.ts     |   5 +
 packages/core/src/__tests__/ai-summarize.test.ts   | 102 +++++++++++++++++++++
 packages/core/src/ai-summarize.ts                  |  85 ++++++++++++-----
 .../src/__tests__/pi-create-fn-agent.test.ts       |  32 +++++++
 packages/engine/src/pi.ts                          |   7 +-
 9 files changed, 233 insertions(+), 23 deletions(-)

Fusion-Task-Id: FN-6218

Fusion-Task-Lineage: 3d6aca32-a56a-43a0-a57b-8e6abc839ce9

packages/engine/src/__tests__/pi-create-fn-agent.test.ts

@@ -30,6 +30,7 @@ const readFileSyncMock = vi.fn((_path?: any) => "{}");
 const realpathSyncNativeMock = vi.fn((path: PathLike) => String(path));
 const readCustomProvidersMock = vi.fn(() => []);
 const packageManagerCwdCapture = vi.fn();
+const packageManagerSettingsCapture = vi.fn();
 
 // Route async `exec` through the `execSync` mock so the promisify bridge works.
 // Use Symbol.for("nodejs.util.promisify.custom") directly to avoid async imports
@@ -107,10 +108,15 @@ vi.mock("@earendil-works/pi-coding-agent", () => ({
     }
   },
   DefaultPackageManager: class {
+    private readonly settingsManager: any;
+
     constructor(options: any) {
       packageManagerCwdCapture(options?.cwd);
+      packageManagerSettingsCapture(options?.settingsManager);
+      this.settingsManager = options?.settingsManager;
     }
     async resolve() {
+      this.settingsManager.isProjectTrusted();
       return packageManagerResolveMock();
     }
   },
@@ -1272,6 +1278,32 @@ describe("createFnAgent", () => {
     expect(createAgentSessionMock).toHaveBeenCalledTimes(1);
   });
 
+  it("exposes project trust on the read-only pi settings view", async () => {
+    const { createReadOnlyPiSettingsView } = await import("../pi.js");
+
+    const view = createReadOnlyPiSettingsView("/tmp", "/mock-agent-dir");
+
+    expect(() => view.isProjectTrusted()).not.toThrow();
+    expect(view.isProjectTrusted()).toBe(true);
+    expect(typeof view.isProjectTrusted()).toBe("boolean");
+  });
+
+  it("passes a project-trusted settings view through package-manager discovery", async () => {
+    const { createFnAgent } = await import("../pi.js");
+
+    await createFnAgent({
+      cwd: "/tmp",
+      systemPrompt: "test",
+      tools: "readonly",
+    });
+
+    const settingsView = packageManagerSettingsCapture.mock.calls.at(-1)?.[0];
+    expect(settingsView).toEqual(expect.objectContaining({ isProjectTrusted: expect.any(Function) }));
+    expect(settingsView.isProjectTrusted()).toBe(true);
+    expect(packageManagerResolveMock).toHaveBeenCalled();
+    expect(createAgentSessionMock).toHaveBeenCalledTimes(1);
+  });
+
   it("registers extension providers before resolving configured models", async () => {
     packageManagerResolveMock.mockResolvedValueOnce({
       extensions: [{ enabled: true, path: "/extensions/zai-provider" }],

packages/engine/src/pi.ts

@@ -1080,6 +1080,7 @@ interface PackageManagerSettingsView {
   getGlobalSettings(): Record<string, any>;
   getProjectSettings(): Record<string, any>;
   getNpmCommand(): string[] | undefined;
+  isProjectTrusted(): boolean;
 }
 
 function readJsonObject(path: string): Record<string, any> {
@@ -1258,7 +1259,7 @@ function siblingAgentDir(agentDir: string, siblingRoot: ".fusion" | ".pi"): stri
   return join(dirname(dirname(agentDir)), siblingRoot, "agent");
 }
 
-function createReadOnlyPiSettingsView(cwd: string, agentDir: string): PackageManagerSettingsView {
+export function createReadOnlyPiSettingsView(cwd: string, agentDir: string): PackageManagerSettingsView {
   const projectRoot = resolvePiExtensionProjectRoot(cwd);
   const fusionAgentDir = agentDir.includes(`${join(".fusion", "agent")}`)
     ? agentDir
@@ -1279,6 +1280,10 @@ function createReadOnlyPiSettingsView(cwd: string, agentDir: string): PackageMan
     getNpmCommand: () => Array.isArray(mergedSettings.npmCommand)
       ? [...mergedSettings.npmCommand]
       : undefined,
+    // Pi's SettingsManager defaults projects to trusted. Fusion workspaces are
+    // user-owned, so preserve pre-upgrade behavior and keep project-scoped
+    // .fusion resources loadable through the read-only settings view.
+    isProjectTrusted: () => true,
   };
 }