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>

tests/test_mcp_tool_systems.py

@@ -73,3 +73,64 @@ async def test_create_task_issue_sets_kind_provenance_and_systems():
     assert kwargs["arose_from_id"] == 9
     systems_svc.set_record_systems.assert_awaited_once_with(1, 50, [2, 3])
     assert result["id"] == 50
+
+
+@pytest.mark.asyncio
+async def test_untagged_hint_names_the_projects_systems():
+    sys_a = MagicMock(); sys_a.id = 1; sys_a.name = "workers"
+    sys_b = MagicMock(); sys_b.id = 2; sys_b.name = "scrape-pipeline"
+    with patch("scribe.mcp.tools.systems.systems_svc") as svc:
+        svc.list_systems = AsyncMock(return_value=[sys_a, sys_b])
+        from scribe.mcp.tools.systems import untagged_systems_hint
+        hint = await untagged_systems_hint(1, 5)
+    assert "workers" in hint and "scrape-pipeline" in hint
+    assert "system_ids" in hint
+    assert "create_system" in hint
+
+
+@pytest.mark.asyncio
+async def test_untagged_hint_absent_without_systems_and_fails_open():
+    from scribe.mcp.tools.systems import untagged_systems_hint
+    with patch("scribe.mcp.tools.systems.systems_svc") as svc:
+        svc.list_systems = AsyncMock(return_value=[])
+        assert await untagged_systems_hint(1, 5) is None
+    with patch("scribe.mcp.tools.systems.systems_svc") as svc:
+        # A hint must never break a create — DB failure degrades to no hint.
+        svc.list_systems = AsyncMock(side_effect=RuntimeError("db down"))
+        assert await untagged_systems_hint(1, 5) is None
+
+
+@pytest.mark.asyncio
+async def test_create_task_untagged_in_project_with_systems_carries_hint():
+    note = MagicMock(); note.id = 60; note.to_dict.return_value = {"id": 60}
+    sys_a = MagicMock(); sys_a.id = 4; sys_a.name = "plugin-hooks"
+    with patch("scribe.mcp.tools.tasks.current_user_id", return_value=1), \
+         patch("scribe.mcp.tools.tasks.notes_svc") as notes_svc, \
+         patch("scribe.mcp.tools.tasks.dedup_svc") as dedup_svc, \
+         patch("scribe.mcp.tools.systems.systems_svc") as hint_svc:
+        notes_svc.create_note = AsyncMock(return_value=note)
+        dedup_svc.find_duplicate_note = AsyncMock(return_value=None)
+        hint_svc.list_systems = AsyncMock(return_value=[sys_a])
+        from scribe.mcp.tools.tasks import create_task
+        result = await create_task(title="untagged", project_id=5)
+    assert "plugin-hooks" in result["systems_hint"]
+
+
+@pytest.mark.asyncio
+async def test_create_task_tagged_or_projectless_carries_no_hint():
+    note = MagicMock(); note.id = 61; note.to_dict.return_value = {"id": 61}
+    with patch("scribe.mcp.tools.tasks.current_user_id", return_value=1), \
+         patch("scribe.mcp.tools.tasks.notes_svc") as notes_svc, \
+         patch("scribe.mcp.tools.tasks.dedup_svc") as dedup_svc, \
+         patch("scribe.mcp.tools.tasks.systems_svc") as systems_svc, \
+         patch("scribe.mcp.tools.systems.systems_svc") as hint_svc:
+        notes_svc.create_note = AsyncMock(return_value=note)
+        dedup_svc.find_duplicate_note = AsyncMock(return_value=None)
+        systems_svc.set_record_systems = AsyncMock()
+        systems_svc.list_record_systems = AsyncMock(return_value=[])
+        hint_svc.list_systems = AsyncMock(return_value=[MagicMock()])
+        from scribe.mcp.tools.tasks import create_task
+        tagged = await create_task(title="tagged", project_id=5, system_ids=[4])
+        orphan = await create_task(title="orphan", project_id=0)
+    assert "systems_hint" not in tagged
+    assert "systems_hint" not in orphan