feat(instructions): fit the delivery fold — 2k server map, floor Systems reflex, write-time systems_hint

Claude Code injects only the first ~2,048 chars of an MCP server's
instructions and silently cuts the rest mid-word (#2562, observed live):
_INSTRUCTIONS was 20,002 chars, so ~90% — including all Systems tagging
guidance — never reached any session. Rearchitect delivery around what
each surface actually delivers:

- _INSTRUCTIONS becomes a 1,997-char purpose-sorted map, with a header
  comment stating the budget and where detail belongs instead.
- Tool docstrings keep the per-tool HOW (audit: nearly all displaced
  topics were already duplicated there); backfill the four gaps —
  enter_project session scoping + project bootstrap, create_rule
  entity-vs-rule test, create_design_system not-a-rulebook,
  create_system two-records test.
- The plugin static context (the delivery floor) gains the
  tag-to-Systems reflex and a surfaces-layering statement; plugin
  0.1.25 -> 0.1.26 so the executing cache refreshes (#2209).
- create_task / create_note / create_snippet return a systems_hint when
  a record is created untagged in a project that has Systems — in-band
  at the exact write it applies to, fail-open like the dedup gate.
- Guards: _INSTRUCTIONS length budget, floor-states-the-reflex, and a
  displaced-topics sweep asserting every cut topic still lives on a
  delivered surface.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/mcp/tools/projects.py

@@ -70,6 +70,19 @@ async def enter_project(project_id: int) -> dict:
     departures from it) plus a summary of the token set — treat it as binding
     for any UI you write, and pull the values with resolve_design_system or
     get_design_system_stylesheet before reaching for a literal.
+
+    Entering a project also SCOPES the session: reference and offer work on
+    this project only, and pass its id to search / list_* so results stay
+    inside it. If something clearly belongs to a different project, say so and
+    ask before switching — never silently operate cross-project. The active
+    project does not stick on the server (each call is self-contained);
+    carrying its id forward is on you.
+
+    Don't wait to be told which project is in scope. When work clearly belongs
+    to a project but none is entered, look for a match yourself (list_projects
+    / search on the repo or subject), propose it, and enter it once the
+    operator confirms; if nothing matches, offer to create one — confirming
+    name and goal first, never guessing a project into existence.
     """
     uid = current_user_id()
     project = await projects_svc.get_project(uid, project_id)