feat(pty): propagate active sessionId and AGENT_TTY_ACTIVE to spawned processes

[prmartinow]

This PR exposes the active session state in the environment of all PTY processes spawned by agent-tty.

Specifically, it injects:

• AGENT_TTY_ACTIVE=true: A simple boolean flag indicating the command is running inside a managed session.
• AGENT_TTY_SESSION_ID=<sessionId>: The UUID of the current terminal session.

Why this is useful:

It enables scripts, shell profiles, and automation utilities running inside the virtual terminal to:

1. Detect the active session and avoid infinite recursion or double-wrapping when invoking shell wrappers.
2. Reference their own session ID programmatically (e.g. to write markers or log annotations).
3. Allow custom prompts or terminal styling to visibly indicate that a session is actively being recorded.

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Code Changes

src/host/hostMain.ts

Passes sessionId from runHost into createPty options.

src/pty/createPty.ts

1. Extends PtyOptions with an optional sessionId field.
2. Updates resolvePtyEnv to accept an optional sessionId.
3. Injects resolved.AGENT_TTY_ACTIVE = 'true' unconditionally.
4. Injects resolved.AGENT_TTY_SESSION_ID = sessionId when a sessionId is provided.

test/unit/pty/createPty.test.ts

Adds Vitest unit tests verifying:

• AGENT_TTY_ACTIVE is unconditionally set to 'true'.
• AGENT_TTY_SESSION_ID is set to the provided value if present.
• AGENT_TTY_SESSION_ID is undefined when no sessionId is passed.

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Verification & Testing

Verify that all repository formats, lints, types, and tests pass:

npm run format:check
npm run lint
npm run typecheck
npm run test
npm run build