feat(telemetry): a usage event records which project the reader was in (#4196, #3735)

`RetrievalLog` has carried `project_id` since it existed, so "this record
was SURFACED on project B" was always answerable. `note_usage_events`
had none, so "this record was OPENED on project B" was not — and the two
cannot be joined to recover it, because there is deliberately no session
identity server-side. NoteUsageEvent's own docstring rules that out.

That gap sat exactly on the question milestone 385 exists to answer. A
lesson's whole claim is that it reaches a session on a project it was not
written on, and step 8's acceptance is "retrieved on a different project
AND opened". Each half was answerable; the conjunction was not.

WHICH project, because the name is ambiguous and the wrong reading makes
the column useless: it is the project the READER was in, never the one
the record belongs to. The record's own project is already on the note;
copying it here would answer a question nobody asked while looking like
it answered this one.

The surfacing half is free — every arm already holds the scope it just
searched, so auto_inject, lesson_slot, the write-path arms and
enter_project now record it. process_skill_sync does not and should not:
it installs every Process the operator can reach, which is not a
project-scoped question, so a project there would be a fiction.

The pull half needs the caller, since a getter knows only what it was
handed. The five single-record getters take `project_id: int = 0` and
pass it through, following the convention `search` and `create_*`
already set. Null stays an ordinary answer meaning "not reported" — a
pull with no project is still a pull and still counts toward dead
weight; it simply cannot speak to transfer. The four REST detail views
report none for now: a human opening a record in a browser is a
different event from an agent recalling one, and #2245 left that
asymmetry deliberately undecided.

Guarded the way #2245 and #2476 taught: by source inspection, because a
parameter that was never threaded through changes no return value and
shows up only as a column that is mysteriously always null. Three
guards — the signature, the pass-through, and the arms — plus the
can-fail test rule 167 asks for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

src/scribe/mcp/tools/snippets.py

@@ -209,7 +209,7 @@ async def create_snippet(
     return data
 
 
-async def get_snippet(snippet_id: int) -> dict:
+async def get_snippet(snippet_id: int, project_id: int = 0) -> dict:
     """Fetch a snippet by id — the full record: code, signature, location, and a
     parsed `snippet` field of its structured parts.
 
@@ -236,6 +236,10 @@ async def get_snippet(snippet_id: int) -> dict:
     `owner` and your `permission`. Read that as ONE PERSON'S SUGGESTION, not as
     established practice here: judge it on its merits, say whose it is when you
     reference it, and don't adopt it as the house pattern without checking.
+
+    `project_id` is the project you are WORKING IN, not this record's own.
+    Passing the active project is what makes "opened away from where it was
+    written" answerable; 0 leaves it unreported and the pull still counts.
     """
     uid = current_user_id()
     note = await snippets_svc.get_snippet(uid, snippet_id)
@@ -250,7 +254,10 @@ async def get_snippet(snippet_id: int) -> dict:
     # snippets_svc.get_snippet — the service is also reached by update/merge
     # paths, and counting those would inflate exactly the number that is
     # supposed to mean "someone chose to look at this" (#2085).
-    record_pulled(user_id=uid, note_id=int(note.id), source="mcp_get_snippet")
+    record_pulled(
+        user_id=uid, note_id=int(note.id),
+        source="mcp_get_snippet", project_id=project_id,
+    )
     await systems_tools.attach_systems(
         uid, note.user_id, data, note.id, note.project_id
     )