feat(cli): path p cache sync — incremental session ingestion

[benbaarber]

What

Adds path p cache sync [types…] — the first step toward a cache that fills itself. It enumerates sessions across the installed agent harnesses and derives into the cache only what is new or changed since the last sync, so users no longer have to p import each session by hand. Groundwork for path query running sync implicitly.

How

• Enumeration reuses cmd_share::gather_sessions (the path share aggregation), filtered per requested harness. No args = all six; path p cache sync claude codex narrows.
• Fingerprint: a session re-derives only when its last_activity or message_count differs from the sync manifest at ~/.toolpath/sync.json ({artifact type → session id → {project?, cache_id, last_activity?, message_count, synced_at}}). Written atomically (temp + rename, 0600), checkpointed after each type so an interrupted first run keeps finished types.
• Derivation goes through new derive_*_session_with variants of the cmd_import helpers that take the provider manager, so listing and derivation agree on provider roots and tests inject fixture resolvers.
• Semantics: sync owns refresh — it overwrites cache entries it re-derives (no --force dance; manual p import keeps error-on-hit). Never deletes: sessions removed upstream keep their cache docs and manifest records (archive, not mirror). Derivation failures warn + tally as failed without aborting.
• Per-type stderr summary (claude 3 new, 1 updated, 240 unchanged); harnesses with no sessions stay silent on default runs.

Numbers (real data, this machine)

34 Claude sessions / 129 MB of JSONL: 5.7 s cold, 0.9 s incremental no-op — and the incremental run correctly caught the one live session that had changed. The 0.9 s floor is the providers' metadata pass (full parse per JSONL file); a stat-level fast path is the planned next optimization before path query runs sync implicitly.

Versioning

path-cli 0.15.0 → 0.16.0 (new subcommand) + toolpath-cli shim bump; workspace deps, site/_data/crates.json, CHANGELOG, CLAUDE.md, README updated per the release checklist. Site builds (11 pages); shim cargo checks.

Tests

• 12 new unit tests in sync.rs: manifest roundtrip + 0600 + corrupt-file hint, first-sync/second-sync/changed-session lifecycle over resolver-injected Claude fixtures, type filtering, refresh-overwrite of unremembered cache entries, failure tallying, provider-missing errors, summary rendering.
• 3 new integration tests: end-to-end ingest → skip → update through the real binary with sandboxed $HOME/$TOOLPATH_CONFIG_DIR; default run with no sessions; unknown-type rejection.
• cargo test --workspace, cargo clippy --workspace -- -D warnings, cargo fmt all clean (includes a drive-by fix for a pre-existing redundant_closure in cmd_export.rs).

Next

Wire path query to run sync before querying (with --no-sync opt-out), then the stat-level enumeration fast path.

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