refactor: codebase audit cleanup — dead code, dedup, module splits

Multi-agent audit + aggressive cleanup across server/web/coder/booterm,
delivered behind a DEFER discipline so none of the in-flight files were
touched. Removes dead code/deps/columns, dedups server + coder helpers,
and splits the oversized modules (tools.ts, opencode-server.ts,
sentinel-summaries, turn.ts, TerminalPane.tsx) behind stable contracts.
Adds 78 parity/unit tests (server 587, coder 323); fixes two latent bugs
(ChatPane queue keys, FileViewerOverlay blank-line parity).

Intended tag: v2.7.12-audit-cleanup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/services/inference/sentinels.ts

@@ -27,6 +27,10 @@ export function detectDoomLoop(
   return { name: ref.name, args: ref.args };
 }
 
+// All sentinel kinds. isAnySentinel and compaction.ts's local predicate both
+// consume this set — single source so a new kind can't be missed in one.
+export const SENTINEL_KINDS = new Set(['cap_hit', 'doom_loop', 'mistake_recovery']);
+
 export function isCapHitSentinel(m: Message): boolean {
   return (
     m.role === 'system' &&
@@ -61,5 +65,10 @@ export function isMistakeRecoverySentinel(m: Message): boolean {
 }
 
 export function isAnySentinel(m: Message): boolean {
-  return isCapHitSentinel(m) || isDoomLoopSentinel(m) || isMistakeRecoverySentinel(m);
+  return (
+    m.role === 'system' &&
+    m.metadata !== null &&
+    typeof m.metadata === 'object' &&
+    SENTINEL_KINDS.has((m.metadata as { kind?: unknown }).kind as string)
+  );
 }