v1.12.4: complete inference.ts split into services/inference/

- sentinel-summaries.ts: runCapHitSummary, insertCapHitSentinel,
  runDoomLoopSummary, insertDoomLoopSentinel
- inference.ts → inference/turn.ts: residue is runAssistantTurn,
  runInference, createInferenceRunner orchestration only
- inference/index.ts: re-export shim preserves the public surface
  (createInferenceRunner, runInference, runAssistantTurn,
  detectDoomLoop, DOOM_LOOP_THRESHOLD, buildMessagesPayload, plus
  type-side InferenceContext/InferenceFrame/StreamResult/TurnArgs/
  FramePublisher)
- src/index.ts + auto_name.ts + the two vitest test files updated to
  import from ./services/inference/index.js explicitly (NodeNext ESM
  doesn't honor directory-index resolution)

Final tally: 11 files under services/inference/, the largest being
sentinel-summaries.ts at 523 LoC (two near-clone summary paths kept
side-by-side until a third sentinel justifies factoring out a shared
runWrapUpSummary). turn.ts is now 326 LoC, the next-largest is
stream-phase.ts at 380. Public import surface unchanged.

tool-phase.ts → turn.ts back-edge for runAssistantTurn remains
(cycle is safe; resolved at call time).

Prepares the file structure for v1.13 AI SDK migration — streamText
swap targets stream-phase.ts only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,20 @@
+// v1.12.4: re-export shim. Outside callers (apps/server/src/index.ts and the
+// vitest inference tests) import from './services/inference/index.js'. The
+// directory is now the public surface; turn.ts holds runAssistantTurn /
+// runInference / createInferenceRunner while the other inference/*.ts files
+// stay implementation-private.
+
+export {
+  createInferenceRunner,
+  runAssistantTurn,
+  runInference,
+} from './turn.js';
+export type {
+  FramePublisher,
+  InferenceContext,
+  InferenceFrame,
+  StreamResult,
+  TurnArgs,
+} from './turn.js';
+export { detectDoomLoop, DOOM_LOOP_THRESHOLD } from './sentinels.js';
+export { buildMessagesPayload } from './payload.js';