Add Pi (pi.dev) agent harness support + shared derive layer

[eliothedeman]

Summary

Adds support for deriving Toolpath provenance documents from Pi coding-agent session logs, and introduces a new shared derivation layer that future conversation providers will build on.

• toolpath-derive (new, 0.1.0) — shared derivation: toolpath_convo::ConversationView → toolpath::v1::Path. Centralizes the turn→step mapping so every provider produces consistent output. toolpath-claude is not migrated in this PR; that's a follow-up so we can validate the shared layer on Pi first.
• toolpath-pi (new, 0.1.0) — read Pi JSONL session files from ~/.pi/agent/sessions/, implement ConversationProvider, and derive Toolpath Path documents. Preserves Pi's in-file conversation tree (id/parentId) as a DAG in the output Path, and follows parentSession links across session files.
• CLI: path derive pi and path list pi, matching the shape of the existing claude/git/github subcommands.

What the new crates do

toolpath-pi layout:

• types.rs — Pi v3 session schema as typed serde enums with forward-compat extra maps on every struct
• paths.rs — PathResolver for ~/.pi/agent/sessions/--<encoded-cwd>--/
• reader.rs — JSONL parser, tree reconstruction via id/parentId, bounded parentSession chain-following
• io.rs — filesystem enumeration (list_projects, list_sessions)
• provider.rs — ConversationProvider impl, tool classification, bash-execution synthesis, tool-result correlation via toolCallId
• derive.rs — thin PiSession → ConversationView → toolpath_derive::derive_path wrapper
• lib.rs — PiConvo manager (default ~/.pi/agent/sessions/, configurable via with_resolver)

toolpath-derive:

• derive_path(view, config) with DeriveConfig { base_uri, path_id, title, include_thinking, include_tool_uses }
• File-path extraction for FileWrite tools uses a fixed field-name preference list: file_path, path, filename, file
• Actors, files_changed, token usage, delegations flow through to PathMeta/step extras

Usage

path derive pi --project /Users/alex/myproj --pretty
path derive pi --project /Users/alex/myproj --session 2026-04-16_abc123
path derive pi --project /Users/alex/myproj --all --pretty
path list pi
path list pi --project /Users/alex/myproj

--base DIR overrides the default ~/.pi/agent/sessions/ on both commands.

Design decisions worth flagging

• No watcher in this PR. Static reading only. A watcher feature parallel to toolpath-claude's can be added later.
• Static classification, no trait hook. Pi tools are classified in toolpath-pi's provider; the shared derive consumes pre-classified ToolCategory only. Keeps the shared layer agnostic of provider tool names/casing.
• Tree preserved as DAG. Pi's in-file branching (id/parentId) maps 1:1 onto Toolpath's dead-end semantics. Dead branches become dead ends in the output Path, exactly as the format intends.
• parentSession cross-file IDs namespaced. Turn IDs from a parent file are rewritten as <session-id>:<entry-id> when merged so they can't collide with child-session IDs.
• toolpath-claude unchanged. Migration onto toolpath-derive is a separate PR.

Test plan

All green:

• cargo test --workspace — 220 existing + 185 new tests, 0 failures
  • toolpath-derive: 30 unit + 1 doc
  • toolpath-pi: 123 unit + 9 integration + 3 doc
  • toolpath-cli: +11 Pi tests (137 total, up from 126)
• cargo clippy -p toolpath-derive -p toolpath-pi --all-targets -- -D warnings — clean
• cargo clippy -p toolpath-cli --bin path -- -D warnings — clean
• path derive pi --help / path list pi --help render correctly
• Manual: run path derive pi against a real ~/.pi/agent/sessions/ directory (reviewer can try)

Release-checklist updates

Per CLAUDE.md's rules for adding new crates, this PR updates:

• Cargo.toml (workspace members + [workspace.dependencies])
• CLAUDE.md (repository layout, dependency graph, CLI examples, testing section, "Things to know")
• README.md (workspace listing)
• site/_data/crates.json + site/pages/crates.md
• scripts/release.sh (tier-2 publish order: toolpath-derive before toolpath-pi)
• CHANGELOG.md

Follow-ups (not in this PR)

1. Migrate toolpath-claude onto toolpath-derive (separate PR; must preserve or justify snapshot deltas).
2. Pi filesystem watcher (feature-gated watcher module mirroring toolpath-claude).

[github-actions]

🔍 Preview deployed: https://50054a6c.toolpath.pages.dev

[eliothedeman]

Basic "rm" of a file in a directory

[akesling]

LGTM