feat(systems): evidence-carrying bootstrap ask for mature zero-Systems projects (#2683)

The generic zero-state systems_hint never converts: identical on every
record, maximal in scope, asked at wrap-up time — Minstrel reached 282
records with zero Systems while vocabularied projects grew organically.
What converts is the project's own evidence at the moment of action.

bootstrap_systems_ask (mcp/tools/systems.py) fires only in a project
with >=20 records and no Systems: it names the record count and recent
titles, and asks for a concrete deliverable — propose 3-6 Systems,
confirm with the operator, create_system the set. Self-retiring: the
first System ends it everywhere. Wired at both moments the task named:
untagged_systems_hint escalates to it at write time, and enter_project
carries it as systems_bootstrap at arrival (attached only when it
applies). Young projects keep the mild question; populated vocabularies
never pay the count query.

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

src/scribe/mcp/tools/projects.py

@@ -17,6 +17,7 @@ keeps working.
 from __future__ import annotations
 
 from scribe.mcp._context import current_user_id
+from scribe.mcp.tools import systems as systems_tools
 from scribe.services import coverage as coverage_svc
 from scribe.services import design_systems as design_systems_svc
 from scribe.services import milestones as milestones_svc
@@ -57,7 +58,8 @@ async def enter_project(project_id: int) -> dict:
 
     Returns a dict with keys: project, milestone_summary, applicable_rules,
     project_rules, subscribed_rulebooks, applicable_rules_truncated,
-    open_tasks, recent_notes, design_system, systems, pattern_coverage.
+    open_tasks, recent_notes, design_system, systems, pattern_coverage —
+    plus systems_bootstrap, present only when it applies (see below).
 
     `pattern_coverage` (usually null) is a one-line estimate of how much of
     the bound repo's code has recorded snippets — e.g. "pattern-library
@@ -72,6 +74,12 @@ async def enter_project(project_id: int) -> dict:
     create it with create_system rather than leaving the area unmodelled. Read
     a subsystem's accumulated records with list_system_records.
 
+    `systems_bootstrap` appears ONLY when the project has many records and no
+    Systems at all — act on it before starting other work: propose a starter
+    vocabulary from the areas the project's records name, confirm it with the
+    operator, and create_system the confirmed set. It stops appearing the
+    moment the first System exists.
+
     `design_system` is null unless the project points at one. When present it
     carries the chain-merged guidance (the house style AND this project's
     departures from it) plus a summary of the token set — treat it as binding
@@ -116,6 +124,17 @@ async def enter_project(project_id: int) -> dict:
     # three days of the feature landing (#2546's audit).
     systems = await systems_svc.list_systems(uid, project_id)
 
+    # The arrival-moment half of the bootstrap ask (#2683): session start is
+    # when the agent has just read the project map and is not yet deep in a
+    # task — the one moment "propose a starter vocabulary" is cheap. The
+    # write-moment half rides untagged-record responses (attach_systems);
+    # both retire the instant the first System exists.
+    systems_bootstrap = None
+    if not systems:
+        systems_bootstrap = await systems_tools.bootstrap_systems_ask(
+            uid, project_id
+        )
+
     # Probably the largest surfacing by volume, and it emitted nothing — so
     # the pulls it caused floated unattributed and the surfaced:pulled ratio
     # ran against a denominator missing its biggest contributor (#2477). An
@@ -143,7 +162,7 @@ async def enter_project(project_id: int) -> dict:
         project.user_id or uid, project_id
     )
 
-    return {
+    out = {
         "project": project.to_dict(),
         "pattern_coverage": coverage_svc.coverage_line(coverage) if coverage else None,
         # Trimmed to what tagging needs. The full charter is get_system's job —
@@ -179,6 +198,11 @@ async def enter_project(project_id: int) -> dict:
             for n in recent_notes
         ],
     }
+    # Attached only when it applies — a key that usually says null trains
+    # readers to skip it (#2483), and this one exists to be acted on.
+    if systems_bootstrap:
+        out["systems_bootstrap"] = systems_bootstrap
+    return out
 
 
 async def get_project(project_id: int) -> dict: