fix(plugin): a compaction clears every session ledger, not the two on the list (#4101)

`scribe_session_context.sh` cleared `.rules.ids` and `.opened.ids` by name and
left `.ids`, `.sync.ids` and `.derive.ids` standing, under a comment asserting
that was a decision. Reading the note arms says it was not: their exclusions go
straight into `semantic_search_notes`, so a surfaced note leaves the result set
rather than being rendered as a reference the way #3750 gave a repeated rule,
and unlike the rules ledger they never age. Hard, permanent, never cleared — a
note surfaced in a session's first minute is unreachable for the rest of it,
which is milestone 386's own defect alive on the arms that fire most often.

The list was the bug, so the fix is not a longer list. `scribe_clear_session_
ledgers` matches the naming convention instead — a per-session ledger is
`<sid>[.<kind>].ids` — which covers all five and covers the sixth on the day it
is written. `<sid>.unreached` is deliberately outside it: that records an
outage, not held context, and #2932 needs it to survive.

tests/test_session_ledger_clear.py runs the hook rather than grepping it for
`rm -f`, since grepping for the names is the pattern being removed. It pins
both directions — `compact`/`clear` take all five, `startup`/`resume` take
none — plus the convention the glob rests on, checked against the hooks
themselves so a ledger named outside it fails loudly instead of silently never
clearing.

Also drops a stale comment pointing at a rules-etag marker that milestone 394
retired.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

plugin/hooks/scribe_defs.sh

@@ -308,6 +308,36 @@ scribe_held_query() {
   return 0
 }
 
+# Drop EVERY per-session ledger, matched by convention rather than listed (#4101).
+#
+# A LIST IS THE BUG. Until now the compact/clear branch named its files one at
+# a time, and it named two of the five: `.rules.ids` and `.opened.ids` were
+# cleared while `.ids` (notes), `.sync.ids` (shape signals) and `.derive.ids`
+# survived. So milestone 386's defect — "a compaction destroys the context but
+# not the ledger, so the most applicable records become permanently
+# unreachable mid-session" — was fixed for rules and left standing on the note
+# and snippet surfaces, which are the ones that fire most often.
+#
+# Nobody decided that. The list was written when rules were the only ledger
+# that mattered and was never revisited when the others arrived, which is what
+# a hand-maintained list of "things to remember to clean up" does. Adding three
+# more `rm` lines would rebuild the same trap for the sixth ledger.
+#
+# So the rule is the NAME: a per-session ledger is `<sid>[.<kind>].ids`, and
+# everything matching that goes. A new ledger following the convention is
+# covered the day it is written, by nobody. One that does not follow it is a
+# deliberate exception and has to say so.
+#
+# Scoped to `.ids` rather than `<sid>.*` so a marker that is REWRITTEN on
+# compact rather than discarded can still live in this directory without
+# being swept away by a glob that was never told about it.
+scribe_clear_session_ledgers() {
+  local dir="$1" sid="$2"
+  [ -n "$dir" ] && [ -n "$sid" ] || return 0
+  rm -f "$dir/$sid"*.ids 2>/dev/null || true
+  return 0
+}
+
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