feat(pi): add Pi (pi.dev) as a sixth CLI run mode (#206)

SessionMode gains 'pi', a first-class backend alongside Claude Code,
OpenCode, Codex, Gemini and Antigravity: its own PTY, tmux session, rose
tab identity, welcome button, run-mode entry, cron agentType, Docker and
remote-SSH command defaults, and clone-repo Brain option.

Pi is a different shape of CLI from the other four, and three decisions
follow from that:

- It has NO permission prompts and no sandbox, so there is no
  --dangerously-skip-permissions analog and none was invented. The
  privilege-shaped knob is the tri-state approveProjectTrust, which makes
  pi load and EXECUTE repo-local .pi/extensions TypeScript and install
  missing project packages. clampExternalCliBypassForOwner() therefore
  puts pi in the MATERIALIZE branch: a non-granted multi-user owner gets
  --no-approve even when no config was sent, because pi's own default is
  a prompt the session user could answer themselves. That helper had zero
  test coverage; it now has coverage for all four CLIs.
- Only the PI_ prefix joins the env allowlist. Pi's ~34 provider key vars
  share no prefix and ALLOWED_ENV_PREFIXES is one global list with no mode
  context, so admitting them would widen the allowlist for every mode at
  once. Auth goes through pi's /login or the server's own environment.
  --api-key is deliberately never wired: it would put a provider secret on
  the spawn command line.
- pi stays OUT of isAltScreenStripMode(). Its default TUI renders into the
  main screen with terminal-owned scrollback, and its 0.84.0 fullscreen
  mode is runtime-switchable via /settings; that flip was measured to put
  the pane into the alt screen, which the strip would have corrupted.

pi-cli-resolver.ts additionally sanity-probes `pi --version` and requires
semver-shaped output, because `pi` is a short generic name a stray binary
can shadow; GET /api/pi/status surfaces path and version so a
misresolution is diagnosable rather than presenting as a broken mode.

Docker installs pi in its own --ignore-scripts step so that flag cannot
affect the other four CLIs, and seeds its credentials per-file rather than
whole-dir (~/.pi/agent also holds sessions, extensions and package trees).

Verified end to end against pi 0.84.1 on an isolated instance: resolver
search-dir fallback, flag construction, piConfig persistence across a full
server restart, the trust prompt and its --no-approve suppression, the
rose Run button on the default daylight-blue skin (the nested skin block
eats per-mode gradients unless the rule lives inside it), and the buffer
local-echo policy, which pi tolerates where codex did not.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/routes/system-routes.test.ts

@@ -86,6 +86,12 @@ vi.mock('../../src/utils/antigravity-cli-resolver.js', () => ({
   resolveAntigravityDir: vi.fn(() => null),
 }));
 
+vi.mock('../../src/utils/pi-cli-resolver.js', () => ({
+  isPiAvailable: vi.fn(() => false),
+  resolvePiDir: vi.fn(() => null),
+  getPiCliVersion: vi.fn(() => null),
+}));
+
 import fs from 'node:fs/promises';
 import { existsSync, readdirSync } from 'node:fs';
 import { subagentWatcher } from '../../src/subagent-watcher.js';
@@ -93,6 +99,7 @@ import { getLifecycleLog } from '../../src/session-lifecycle-log.js';
 import { isOpenCodeAvailable, resolveOpenCodeDir } from '../../src/utils/opencode-cli-resolver.js';
 import { isGeminiAvailable, resolveGeminiDir } from '../../src/utils/gemini-cli-resolver.js';
 import { isAntigravityAvailable, resolveAntigravityDir } from '../../src/utils/antigravity-cli-resolver.js';
+import { isPiAvailable, resolvePiDir, getPiCliVersion } from '../../src/utils/pi-cli-resolver.js';
 
 const mockedReadFile = vi.mocked(fs.readFile);
 const mockedWriteFile = vi.mocked(fs.writeFile);
@@ -106,6 +113,9 @@ const mockedIsGeminiAvailable = vi.mocked(isGeminiAvailable);
 const mockedResolveGeminiDir = vi.mocked(resolveGeminiDir);
 const mockedIsAntigravityAvailable = vi.mocked(isAntigravityAvailable);
 const mockedResolveAntigravityDir = vi.mocked(resolveAntigravityDir);
+const mockedIsPiAvailable = vi.mocked(isPiAvailable);
+const mockedResolvePiDir = vi.mocked(resolvePiDir);
+const mockedGetPiCliVersion = vi.mocked(getPiCliVersion);
 
 describe('system-routes', () => {
   let harness: RouteTestHarness;
@@ -839,6 +849,38 @@ describe('system-routes', () => {
     });
   });
 
+  // ========== GET /api/pi/status ==========
+
+  describe('GET /api/pi/status', () => {
+    it('returns unavailable when pi is not installed', async () => {
+      mockedIsPiAvailable.mockReturnValue(false);
+      mockedResolvePiDir.mockReturnValue(null);
+      mockedGetPiCliVersion.mockReturnValue(null);
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/pi/status' });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.available).toBe(false);
+      expect(body.path).toBeNull();
+      expect(body.version).toBeNull();
+    });
+
+    it('returns available with path AND version when pi is installed', async () => {
+      // `version` is pi-specific: `pi` is a generic binary name, so the resolver
+      // version-probes it and this endpoint is where a misresolution shows up.
+      mockedIsPiAvailable.mockReturnValue(true);
+      mockedResolvePiDir.mockReturnValue('/home/user/.local/bin');
+      mockedGetPiCliVersion.mockReturnValue('0.84.1');
+
+      const res = await harness.app.inject({ method: 'GET', url: '/api/pi/status' });
+      expect(res.statusCode).toBe(200);
+      const body = JSON.parse(res.body);
+      expect(body.available).toBe(true);
+      expect(body.path).toBe('/home/user/.local/bin');
+      expect(body.version).toBe('0.84.1');
+    });
+  });
+
   // ========== GET /api/execution/model-config ==========
 
   describe('GET /api/execution/model-config', () => {