feat(rules)!: retire the always-on tier — every rule arrives by retrieval (#394)

Milestone 394, steps 5-8. Operator: "remove the always on rule functionality
as the goal was to not have it at all since it didn't seem to work as
expected."

Unconditional preload had three failures the retrieval arms do not. It could
not be MEASURED — a resident rule is in the context whether or not it
mattered, so nothing distinguished "this governed the act" from "this was
scenery", and it was the one surface structurally exempt from the scoreboard
judging every other. It was SUMMARISED AWAY by compaction while the session
went on believing it held the rules. And it CROWDED OUT the few rules that
applied with the thirty that did not.

WHAT GOES

Schema (0100): rules.tier + ck_rules_tier, rule_versions.tier,
rulebooks.always_on, and project_rulebook_exclusions — a table recording a
project's opt-out of something that no longer binds it unasked.

Tools: list_always_on_rules, exclude_always_on_rulebook,
include_always_on_rulebook. Service: the same three plus rules_etag_for,
_valid_tier and the whole etag family. The SessionStart preload and the
write-path staleness arm go with them: nothing is resident, so nothing can
have drifted since a session loaded it.

THREE CALLS WORTH REVIEWING

enter_project got NARROWER, not wider. Its filter was `always_on OR
area-tagged`; dropping the tier arm leaves the deterministic half, so a
project with no canonical-tagged Systems gets no bulk rules and reaches them
by retrieval instead. Dropping the whole clause would have made that payload
bigger than the preload this milestone deletes.

Backups import tolerantly. A pre-394 archive carries tier, always_on and the
retired inception choice; none is read, and the exclusion key is DROPPED
rather than remapped, because restoring it would write data that
validate_inception now rejects as unknown.

The migration is irreversible in the way that matters and says so: downgrade
recreates the columns at their defaults and cannot restore which rules were
always-on. A value invented to fill a hole is not a measurement.

THE INSTRUCTION SURFACES SAY THE HARDER THING

Deleting "call list_always_on_rules()" is easy; replacing it is not, because
the new model asks a session to trust something it cannot see. All three
surfaces now say a session holds nothing, that rules arrive when work matches
them, and — the half that got dangerous — that "no rule arrived" means
"nothing matched", never "there is no rule". Under residency an empty session
was rare and suspicious; it is now the ordinary state of most turns, so
reading it as permission is wrong on nearly every turn rather than
occasionally. That is #3720's defect at session scale.

test_instruction_surfaces_agree is repointed rather than retired: its two
halves collapsed into one instruction, and it gains a guard that every
surface states what absence means. _INSTRUCTIONS is back at 1999/2000 —
the inception clause paid for the longer HOW line.

UI (rule 27, and the opportunity step 8 named)

The tier selector is gone, and what replaces it is the point: `when_to_apply`
is now the field that decides whether a rule is ever seen, so the editor
marks it required, warns while it is empty, and both rule lists badge a
trigger-less rule "never surfaces". A rule without one is not quiet, it is
unreachable.

TESTS

Two files deleted outright — test_rules_etag.py and test_inception_rules.py
tested subsystems that no longer exist. Elsewhere obsolete cases were removed
and the rest repointed. One deserves naming: the wiring test asserted the act
arms pass no `tier`, which had become an assertion that could not fail. It is
repointed onto `kind`, which does still exist and where the same claim is
live — a preference must reach a write exactly as a rule does.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011cPyzNnegXHr5iRMzzy5KJ

tests/test_services_plugin_context.py

@@ -4,23 +4,9 @@ import pytest
 from tests.helpers import fake_note
 
 
-@pytest.fixture(autouse=True)
-def _no_exclusions():
-    """build_session_context asks for the bound project's always-on
-    exclusions (milestone 297); these tests script the rules only."""
-    with patch("scribe.services.plugin_context.rulebooks_svc.excluded_always_on_rulebooks",
-               AsyncMock(return_value=[])):
-        yield
-
-
 pytestmark = pytest.mark.usefixtures("_no_supersession")
 
 
-def _rule(rid, title, topic_id):
-    r = MagicMock()
-    r.id, r.title, r.topic_id = rid, title, topic_id
-    r.statement = "FULL STATEMENT SHOULD NOT BE INJECTED"
-    return r
 
 
 # ─── knowledge auto-inject (Path A) ──────────────────────────────────────────
@@ -106,30 +92,6 @@ async def test_build_autoinject_hint_blank_query_returns_empty():
     search.assert_not_called()
 
 
-@pytest.mark.asyncio
-async def test_build_session_context_renders_titles_grouped_by_topic():
-    rules = [
-        _rule(1, "`dev` is home", 1),
-        _rule(2, "Release — never without explicit request", 1),
-        _rule(3, "No GitHub — Fabled-Git only", 2),
-    ]
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=rules)), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow", 2: "fabled-git"})):
-        from scribe.services.plugin_context import build_session_context
-        out = await build_session_context(user_id=7, project_id=0)
-
-    ctx = out["context"]
-    assert out["rule_count"] == 3
-    assert out["project"] is None
-    # Titles present, grouped under topic headings
-    assert "### git-workflow" in ctx
-    assert "### fabled-git" in ctx
-    assert "- [1] `dev` is home" in ctx
-    assert "- [3] No GitHub — Fabled-Git only" in ctx
-    # Full statements must NOT be dumped (push channel injects titles only)
-    assert "FULL STATEMENT SHOULD NOT BE INJECTED" not in ctx
 
 
 @pytest.mark.asyncio
@@ -139,11 +101,7 @@ async def test_build_session_context_includes_project_when_scoped():
     # opposite of what this test is about.
     project = MagicMock(id=2, title="FabledScribe", goal="ship it",
                         design_system_id=None)
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=[_rule(1, "rule", 1)])), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow"})), \
-         patch("scribe.services.plugin_context.projects_svc.get_project",
+    with patch("scribe.services.plugin_context.projects_svc.get_project",
                AsyncMock(return_value=project)), \
          patch("scribe.services.plugin_context.notes_svc.list_notes",
                AsyncMock(return_value=([], 4))):
@@ -170,11 +128,7 @@ async def test_build_session_context_pushes_the_projects_design_system():
         "guidance": [], "token_count": 95,
         "token_groups": ["accent", "surface", "type"],
     }
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=[_rule(1, "rule", 1)])), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow"})), \
-         patch("scribe.services.plugin_context.projects_svc.get_project",
+    with patch("scribe.services.plugin_context.projects_svc.get_project",
                AsyncMock(return_value=project)), \
          patch("scribe.services.plugin_context.notes_svc.list_notes",
                AsyncMock(return_value=([], 0))), \
@@ -200,11 +154,7 @@ async def test_build_session_context_survives_an_unreadable_design_system():
     That must degrade to "no design block", not to a crash that costs the
     session its rules too."""
     project = MagicMock(id=2, title="App", goal="", design_system_id=9)
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=[_rule(1, "rule", 1)])), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow"})), \
-         patch("scribe.services.plugin_context.projects_svc.get_project",
+    with patch("scribe.services.plugin_context.projects_svc.get_project",
                AsyncMock(return_value=project)), \
          patch("scribe.services.plugin_context.notes_svc.list_notes",
                AsyncMock(return_value=([], 0))), \
@@ -219,14 +169,10 @@ async def test_build_session_context_survives_an_unreadable_design_system():
 
 @pytest.mark.asyncio
 async def test_build_session_context_unbound_repo_emits_bind_hint():
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=[_rule(1, "rule", 1)])), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow"})):
-        from scribe.services.plugin_context import build_session_context
-        out = await build_session_context(
-            user_id=7, project_id=0, unbound_repo="host/owner/repo",
-        )
+    from scribe.services.plugin_context import build_session_context
+    out = await build_session_context(
+        user_id=7, project_id=0, unbound_repo="host/owner/repo",
+    )
 
     ctx = out["context"]
     assert out["project"] is None
@@ -289,16 +235,29 @@ async def test_build_process_manifest_truncates_long_preview():
 
 @pytest.mark.asyncio
 async def test_build_session_context_caps_length():
-    many = [_rule(i, "x" * 200, 1) for i in range(200)]
-    with patch("scribe.services.plugin_context.rulebooks_svc.list_always_on_rules",
-               AsyncMock(return_value=many)), \
-         patch("scribe.services.plugin_context._topic_titles",
-               AsyncMock(return_value={1: "git-workflow"})):
-        from scribe.services.plugin_context import build_session_context
-        out = await build_session_context(user_id=7)
+    """The cap still binds, and now has to be provoked rather than tripped.
 
-    assert len(out["context"]) <= 9000 + 60  # cap + truncation note
-    assert "truncated" in out["context"]
+    This used to hand the block 200 long rule titles, because the preload made
+    overflow the easy case. Milestone 394 removed that block, so nothing this
+    function assembles on its own is big enough any more — which is a reason
+    to drive the cap directly, not a reason to drop it. The project and design
+    blocks are still unbounded in principle, and the hook passes this text
+    through verbatim.
+
+    Patching the cap rather than manufacturing 9,000 characters keeps the test
+    about the TRUNCATION PATH — that it cuts, and that it says it cut — which
+    is the part a reader depends on.
+    """
+    from scribe.services import plugin_context as pc
+
+    with patch.object(pc, "_MAX_CHARS", 120):
+        out = await pc.build_session_context(user_id=7)
+
+    assert len(out["context"]) <= 120 + 60  # cap + truncation note
+    assert "truncated" in out["context"], (
+        "the block was cut without saying so — a reader cannot tell a "
+        "truncated context from a short one"
+    )
 
 
 # --- the reuse slot (#2246) --------------------------------------------------