feat(storage): add session-global scope for tasks outside the workspace

[tintinweb]

Based on @kunaaal13's #61, included here as the first commit. #61 changed the default and migrated existing files; this reworks it as an opt-in so that nothing changes for anyone who does not ask for it.

The problem

taskScope: "session" — the default since v0.3.3 — writes <workspace>/.pi/tasks/tasks-<sessionId>.json, so every repository pi runs in picks up an untracked directory holding a file keyed by a session ID. That data is of no use to anyone else cloning the project, and it costs a .gitignore rule per repository.

What changes for existing users

Nothing. session stays the default and writes exactly where it always has. No file is moved, copied, or deleted on upgrade, and there is no migration step.

	Before	After
session (default)	<workspace>/.pi/tasks/tasks-<sessionId>.json	unchanged
project	<workspace>/.pi/tasks/tasks.json	unchanged
memory	in-memory	unchanged
PI_TASKS — off, named, absolute, relative		unchanged
PI_TASKS=sprint-1	~/.pi/tasks/sprint-1.json	unchanged

src/task-store.ts is byte-identical to master.

What is added

A fourth taskScope value, session-global. Same per-session isolation and resume behaviour as session, but the file is kept outside the workspace:

<agent-dir>/tasks/sessions/<project-key>/tasks-<sessionId>.json

<agent-dir> is ~/.pi/agent unless pi is configured otherwise, so the file follows PI_CODING_AGENT_DIR like every other piece of user-level state. <project-key> uses the same workspace encoding pi applies to its own session logs (/Users/me/work/repo → --Users-me-work-repo--), so a project's task files sit under the same name as its transcripts, and same-ID sessions in different workspaces cannot collide.

Picking it

Via /tasks → Settings → Task storage, which now cycles memory → session → session-global → project. Takes effect on the next session start.

Note that the settings menu writes project overrides to <workspace>/.pi/tasks-config.json, so choosing it there still leaves a .pi/ in that repository — holding config rather than task data. To apply it everywhere and leave repositories untouched, set it once in <agent-dir>/tasks-config.json:

{ "taskScope": "session-global" }

Opting in does not move anything either

session-global changes where new session files are created. A session that already has a file in <workspace>/.pi/tasks/ keeps being read and written there, so:

• resuming an existing session still finds its tasks;
• switching back to session strands nothing;
• no sweep, no copy, no delete — the migration logic from fix(storage): keep session tasks outside workspaces #61 is removed entirely.

The trade-off is explicit: opting in does not clean up a repository that already has session files. Those disappear the normal way, when their lists are cleared. A union read across both locations was considered and rejected — nextId is a per-file counter and IDs are String(this.nextId++), so both files independently contain a task "1"; the lock guards one path; and a delete would resurrect from the other side.

Under session-global only, an emptied session directory is removed so global storage does not accumulate one empty directory per workspace ever opened. <workspace>/.pi/tasks/ is left standing exactly as before.

Testing

Covered: the default scope writing into the workspace and creating nothing under the agent directory; session-global keeping a new session out of the workspace; an existing workspace file still being used and written to after opting in; directory reclamation; a relocated PI_CODING_AGENT_DIR; and the workspace encoding.

Two fixes unrelated to the behaviour above:

• The suite read and wrote the real ~/.pi/ of whoever ran it, inheriting their global settings and leaving files behind. HOME now points at a scratch directory for the run and PI_CODING_AGENT_DIR is cleared — getAgentDir() consults it first, so redirecting the home directory alone would not have contained a contributor who has it set.
• vitest.config.ts is excluded from the published tarball; it refers to test/, which is not shipped.

npm run lint       passed
npm run typecheck  passed
npm run test       361 passed
npm run build      passed

Supersedes #61.

closes #57
closes #53