session-snapshot

# Session Snapshot Shared snapshot primitive for `/lets:end` (settlement + snapshot) and for the snapshot-only flags `--session` and `--pre-compact` on both `/lets:end` and `/lets:note`. **Single source of truth** - every caller delegates here so the template and file/pointer behavior never drift. Goal: ONE recovery-grade `## RESUME` snapshot, **file-primary** - it ALWAYS lands in a `.lets/sessions/` file (the single trail `/lets:start` reads), regardless of task state (feature / trunk / --main / no-task). The active task gets only a ONE-LINE pointer to that file, and only when a task is unambiguously active (via detect-task, NEVER a `list-by-status | head -1` guess). > **Contract - this skill ONLY writes the snapshot (file + optional pointer).** It does NOT end the session, push, merge, commit, or close anything. The caller decides what else to do. ## Arguments (from the caller) Passed via the `Skill` invocation's `args` string as space-separated `key=value` pairs (e.g. `args: "kind=end pointer=off task-id=lets-abc range=session: X..HEAD (3 commits)"`). Put `range=` / `task-id=` LAST when the value contains spaces - each consumes the rest of the string. Any omitted key falls to its default. - `kind` = `precompact` (default) | `session` | `end` - selects the `artifact-path` kind and the `### Compaction` line. `precompact` -> `snapshot-precompact`; `session` and `end` BOTH -> `snapshot`, because a session record and a session-end record are the same artifact written at d...