feat(rulings): a command or edit touching an area's files shows its rulings, once per session (milestone 444 step 4, #4757)

A System's rulings (the Rulings section of its description) now reach the
work by path, not by similarity. Both PreToolUse arms resolve the files a
command or edit names to the Systems whose path_patterns cover them, and the
first touch in a session shows each area's rulings in one line; a repeat is
a one-line reference. A lookup, so no floor, no budget, no retrieval_logs row.

- services/system_rulings: parse_rulings, command_paths (reads and writes,
  relative to the repo root from any cwd; flags, URLs, globs skipped),
  rulings_for_paths
- /tool-rules takes root, cwd and seen_ruling_systems; /prior-art takes
  seen_ruling_systems; both return ruling_system_ids
- hooks share <sid>.rulings.ids (cleared on compaction by the ledger naming
  convention); the Bash hook sends the repo root and cwd
- system_usage_events (migration 0114): surfacings by source, pulls from
  get_system; carried by backup (v20) through the system map
- writing-records: rulings also arrive when the area's files are touched

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_services_backup.py

@@ -27,7 +27,7 @@ def test_backup_version_is_current():
 
     (Named for the number it asserted until v10, which is exactly the drift a
     name-carrying-a-value invites; it now says what it checks.)"""
-    assert backup.BACKUP_VERSION == 19
+    assert backup.BACKUP_VERSION == 20
 
 
 def _exportable_note(**over):
@@ -139,6 +139,7 @@ def _column_guard_targets():
     from scribe.models.note_supersession import NoteSupersession
     from scribe.models.note_usage import NoteUsageEvent
     from scribe.models.rule_usage import RuleUsageEvent
+    from scribe.models.system_usage import SystemUsageEvent
     from scribe.models.retrieval_tuning import RetrievalTuningEvent
     from scribe.models.note_version import NoteVersion
     from scribe.models.rule_version import RuleVersion
@@ -172,6 +173,7 @@ def _column_guard_targets():
         "lesson_no_rule": (LessonNoRule, backup._lesson_no_rule_rows),
         "note_usage_events": (NoteUsageEvent, backup._usage_event_rows),
         "rule_usage_events": (RuleUsageEvent, backup._rule_usage_event_rows),
+        "system_usage_events": (SystemUsageEvent, backup._system_usage_event_rows),
         "retrieval_tuning_events": (
             RetrievalTuningEvent, backup._retrieval_tuning_event_rows,
         ),
@@ -290,6 +292,7 @@ def _import_guard_targets():
         "lesson_no_rule": backup._build_lesson_no_rule,
         "note_usage_events": backup._build_usage_event,
         "rule_usage_events": backup._build_rule_usage_event,
+        "system_usage_events": backup._build_system_usage_event,
         "retrieval_tuning_events": backup._build_retrieval_tuning_event,
         "design_systems": backup._build_design_system,
         "design_tokens": backup._build_design_token,
@@ -543,7 +546,9 @@ async def test_export_full_backup_contains_every_declared_section():
                 # v18: which rule each lesson is an instance of.
                 "lesson_rule_links",
                 # v19: the lessons judged to fall under no rule.
-                "lesson_no_rule"):
+                "lesson_no_rule",
+                # v20: whether an area's rulings were read once shown.
+                "system_usage_events"):
         assert key in out, f"missing export section: {key}"
         assert out[key] == []