feat(acl): shared records are search-only and always labelled as someone else's

Narrows the b7d6fc7 widening per the operator's call, and fixes a regression it
introduced. Decision recorded as note 2094.

Two scopes now, deliberately different:

  readable_notes_clause  — everything the ACL permits, including records reached
                           only via a direct/group note share. For EXPLICIT acts:
                           a search the caller typed, a fetch by id.
  browsable_notes_clause — the caller's own records plus anything in a project
                           they can reach. For PASSIVE surfaces: browse lists,
                           facet counts, the process->skill manifest.

The split is a trust boundary. Anything appearing unasked — in your own list,
your own counts, or as a skill installed on your machine — reads as material you
endorsed. A one-off someone shared with you hasn't earned that standing, so it
waits until you go looking. This also dissolves the shared-Process problem by
construction rather than by special case: the manifest is a passive surface, so a
directly-shared Process is never installed as an auto-surfacing skill.

Regression fix (#2093): b7d6fc7 widened the list queries but left the fetch path
owner-only, so on the MCP path a record could be listed and then not opened —
get_snippet raised not-found, get_process couldn't resolve, and the manifest
emitted stubs whose get_process call would fail. snippets.get_snippet and
notes.resolve_process now resolve the read scope. delete_snippet gained an
explicit can_write_note guard, since being able to SEE a shared snippet must not
imply being able to bin it.

Provenance, so nothing arrives looking like the operator's own work:
- access.describe_provenance / label_shared_items add shared/owner/permission;
  labelling costs no query when everything is the caller's own.
- MCP: get_snippet, list_snippets, get_process and list_processes carry it, and
  get_process now says outright NOT to follow a shared process verbatim — its
  follow-as-written contract was the sharpest instance of the problem.
- The skill stub for a shared Process names its author and asks for a go-ahead,
  instead of describing it as "the operator's saved Scribe process".
- Policy stated once in the MCP _INSTRUCTIONS and the reusing-code skill: a
  shared record is that person's suggestion, weigh it, attribute it, ask before
  adopting it.
- UI: shared snippets show "by <owner>" in the list and a notice above the code
  in the detail view, reusing SharedWithMeView's vocabulary.

Plugin 0.1.15 -> 0.1.16 (skill text changed).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLwAaV4DQEmVyn496HnEvt

src/scribe/services/notes.py

@@ -412,15 +412,23 @@ async def convert_task_to_note(user_id: int, note_id: int) -> Note:
 async def resolve_process(user_id: int, name_or_id) -> tuple[Note | None, list[dict]]:
     """Resolve a stored process by id or name.
 
-    Owner-scoped, note_type='process', non-trashed. Precedence: numeric id →
-    exact case-insensitive title → substring. Returns (note, other_candidates);
-    on a substring tie with no exact hit, `note` is the most-recently-updated
-    match and `other_candidates` lists the rest as [{id, title}] so the caller
-    can disambiguate. Returns (None, []) when nothing matches.
+    note_type='process', non-trashed, scoped to what this user may READ — owned
+    plus shared (rule #78). Naming one is an explicit act, so a Process shared
+    with the caller resolves here even though it is deliberately absent from the
+    passive process list and the skill manifest (decision note 2094); without
+    this, a Process a search surfaced could not then be run — see #2093.
+
+    Precedence: numeric id → exact case-insensitive title → substring. Returns
+    (note, other_candidates); on a substring tie with no exact hit, `note` is the
+    most-recently-updated match and `other_candidates` lists the rest as
+    [{id, title}] so the caller can disambiguate. Returns (None, []) when nothing
+    matches.
     """
+    from scribe.services.access import readable_notes_clause
+    visible = await readable_notes_clause(user_id)
     async with async_session() as session:
         base = select(Note).where(
-            Note.user_id == user_id,
+            visible,
             Note.note_type == "process",
             Note.deleted_at.is_(None),
         )