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>

src/types/session.ts

@@ -8,13 +8,14 @@
  * - SessionConfig — creation-time config (id, workingDir, createdAt)
  * - SessionOutput — captured stdout/stderr/exitCode
  * - SessionStatus — 'idle' | 'busy' | 'stopped' | 'error'
- * - SessionMode — 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini' | 'antigravity' (which CLI backend)
+ * - SessionMode — 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini' | 'antigravity' | 'pi' (which CLI backend)
  * - ClaudeMode — CLI permission mode ('dangerously-skip-permissions' | 'auto' | 'normal' | 'allowedTools')
  * - SessionColor — visual differentiation color
  * - OpenCodeConfig — OpenCode-specific settings (model, autoAllowTools, continueSession)
  * - CodexConfig — Codex (OpenAI CLI)-specific settings (model, resumeSessionId)
  * - GeminiConfig — Gemini CLI-specific settings (model, approvalMode, resumeSession)
  * - AntigravityConfig — Antigravity CLI (agy) settings (model, dangerouslySkipPermissions, resumeConversationId)
+ * - PiConfig — Pi CLI (pi.dev) settings (model, provider, thinking, resume/continue, project trust)
  *
  * Cross-domain relationships:
  * - SessionState.respawnConfig embeds RespawnConfig (respawn domain)
@@ -43,11 +44,11 @@ export type SessionStatus = 'idle' | 'busy' | 'stopped' | 'error';
 export type ClaudeMode = 'dangerously-skip-permissions' | 'auto' | 'normal' | 'allowedTools';
 
 /** Session mode: which CLI backend a session runs */
-export type SessionMode = 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini' | 'antigravity';
+export type SessionMode = 'claude' | 'shell' | 'opencode' | 'codex' | 'gemini' | 'antigravity' | 'pi';
 
 export type RemoteCommandMode = Extract<
   SessionMode,
-  'shell' | 'claude' | 'opencode' | 'codex' | 'gemini' | 'antigravity'
+  'shell' | 'claude' | 'opencode' | 'codex' | 'gemini' | 'antigravity' | 'pi'
 >;
 
 /**
@@ -156,7 +157,7 @@ export interface RemoteSessionInfo {
 /** Which CLI backends a Docker case can run (same set as remote). */
 export type DockerCommandMode = Extract<
   SessionMode,
-  'shell' | 'claude' | 'opencode' | 'codex' | 'gemini' | 'antigravity'
+  'shell' | 'claude' | 'opencode' | 'codex' | 'gemini' | 'antigravity' | 'pi'
 >;
 
 /** Container engine. Docker and Podman differ in the uid/userns + host-gateway alias. */
@@ -331,6 +332,37 @@ export interface AntigravityConfig {
   resumeConversationId?: string;
 }
 
+/**
+ * Pi CLI (pi.dev) session configuration.
+ *
+ * Pi has NO permission prompts and no `--dangerously-skip-permissions` analog,
+ * so there is deliberately no bypass field here. The one privilege-shaped knob is
+ * `approveProjectTrust`, which controls whether pi loads and EXECUTES repo-local
+ * `.pi/` extensions (and installs missing project packages).
+ */
+export interface PiConfig {
+  /** Model pattern or ID. Supports `provider/id` and a `:<thinking>` suffix (e.g. `sonnet:high`). Passed via --model. */
+  model?: string;
+  /** Provider name (anthropic, openai, google, ...). Passed via --provider. */
+  provider?: string;
+  /** Reasoning level. Passed via --thinking. */
+  thinking?: 'off' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh' | 'max';
+  /** Continue the most recent session (-c). Skipped when resumeSessionId is set (the two conflict). */
+  continueSession?: boolean;
+  /** Resume a specific session by ID or partial UUID (--session). Ids only, never paths. */
+  resumeSessionId?: string;
+  /**
+   * Tri-state project trust (repo-local `.pi/` settings/extensions/skills, plus
+   * installing missing project packages):
+   *   true   -> --approve    (trust for this run; loads and EXECUTES repository TypeScript)
+   *   false  -> --no-approve (force-deny; the trust prompt never appears)
+   *   absent -> pi's own defaultProjectTrust (ask).
+   * Multi-user: MATERIALIZED to false for non-granted owners, because pi's
+   * absent-config default is a prompt the session user could answer themselves.
+   */
+  approveProjectTrust?: boolean;
+}
+
 /**
  * Configuration for creating a new session
  */
@@ -484,6 +516,8 @@ export interface SessionState {
   geminiConfig?: GeminiConfig;
   /** Antigravity-specific configuration (only for mode === 'antigravity') */
   antigravityConfig?: AntigravityConfig;
+  /** Pi-specific configuration (only for mode === 'pi') */
+  piConfig?: PiConfig;
   /** Claude conversation session ID to resume after reboot (set by restore script) */
   resumeSessionId?: string;
   /** Claude CLI effort level (soft default via --settings, switchable in-session via /effort) */