feat(inception): always-on exclusions reach every rule surface — list_always_on_rules(project_id), get_applicable_rules, rules_payload.excluded_always_on, session context, exclude/include tools (#2880, milestone 297 step 2)

A project that opted out of an always-on rulebook at inception must not see
it anywhere: list_always_on_rules(project_id=) and the subscription-derived
set skip it (an exclusion is total), get_applicable_rules / rules_payload
carry `excluded_always_on` as the seventh key so the departure is visible
wherever the rules are, and the SessionStart block built for a bound project
names it ("Excluded for this project by its inception decision …"). MCP:
list_always_on_rules takes project_id; exclude_always_on_rulebook /
include_always_on_rulebook mirror suppress/unsuppress (owner-only; the
rulebook must be always_on — subscribed rulebooks are left by unsubscribing).

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

src/scribe/mcp/tools/rulebooks.py

@@ -222,16 +222,22 @@ async def list_rules(
     return {"rules": [_rule_summary(r) for r in rows], "total": len(rows)}
 
 
-async def list_always_on_rules() -> dict:
+async def list_always_on_rules(project_id: int = 0) -> dict:
     """Return all rules from rulebooks flagged always_on for the current user.
 
     Call this at session start. Treat the returned rules as binding for the
     session — they apply regardless of which project (if any) is in scope.
     Pair with get_project(id).applicable_rules when working on a specific
     project to also load that project's subscription-derived rules.
+
+    Args:
+        project_id: 0 (default) = the user-wide set. Inside a project, pass
+            its id: an always-on rulebook the project EXCLUDED at inception
+            (see enter_project's `excluded_always_on`) is left out — the
+            project decided not to inherit it.
     """
     uid = current_user_id()
-    rules = await rulebooks_svc.list_always_on_rules(uid)
+    rules = await rulebooks_svc.list_always_on_rules(uid, project_id=project_id)
     return {"rules": [_rule_summary(r) for r in rules], "total": len(rules)}
 
 
@@ -407,6 +413,35 @@ async def unsubscribe_project_from_rulebook(
 
 # ── Suppressions — project-level mute of rulebook rules / topics ────────
 
+async def exclude_always_on_rulebook(project_id: int, rulebook_id: int) -> dict:
+    """Opt a project OUT of a whole always-on rulebook (milestone 297).
+
+    Always-on rulebooks bind every project implicitly; an inception decision
+    can say "not this one, not here". The exclusion is total for that project
+    — list_always_on_rules(project_id), enter_project/get_project rules and
+    the session-start context all leave it out and name it under
+    `excluded_always_on`. Owner-only; the rulebook must be always_on (a
+    subscribed rulebook is left with unsubscribe_project_from_rulebook).
+    Idempotent; include_always_on_rulebook reverses it. Normally reached via
+    decide_project_inception, not by hand.
+    """
+    uid = current_user_id()
+    await rulebooks_svc.exclude_always_on_rulebook_for_project(
+        project_id=project_id, rulebook_id=rulebook_id, user_id=uid,
+    )
+    return {"project_id": project_id, "rulebook_id": rulebook_id, "excluded": True}
+
+
+async def include_always_on_rulebook(project_id: int, rulebook_id: int) -> dict:
+    """Reverse exclude_always_on_rulebook: the always-on rulebook binds this
+    project again. Idempotent."""
+    uid = current_user_id()
+    await rulebooks_svc.include_always_on_rulebook_for_project(
+        project_id=project_id, rulebook_id=rulebook_id, user_id=uid,
+    )
+    return {"project_id": project_id, "rulebook_id": rulebook_id, "excluded": False}
+
+
 async def suppress_rule_for_project(
     project_id: int, rule_id: int,
 ) -> dict:
@@ -470,5 +505,6 @@ def register(mcp) -> None:
         subscribe_project_to_rulebook, unsubscribe_project_from_rulebook,
         suppress_rule_for_project, unsuppress_rule_for_project,
         suppress_topic_for_project, unsuppress_topic_for_project,
+        exclude_always_on_rulebook, include_always_on_rulebook,
     ):
         mcp.tool(name=fn.__name__)(fn)