PR-D1 (ADR 0008 Phase D): remove ADR 0007 server-side dead code

[FluffyAIcode]

What

ADR 0008 §6.4 PR-D1 originally proposed two coupled changes:

1. Remove ADR-0007-vintage server dead code.
2. Refactor the HTTP shim onto SessionStore.

Implementation revealed (1) is a pure subtraction with no behavior dependence on (2), so they're split — same pattern as PR-A3 / PR-A3b. This PR is (1). PR-D2 (queued, not in this diff) is (2).

ADR 0008 §6.4 amended in this PR to record the split.

Net diff: −540 / +78

9 files changed, 78 insertions(+), 540 deletions(-)

Files (production)

File	Δ	What was removed
inference_engine/server/engine.py	−12	EngineResult.path_selection / .tokens_skipped / .prefill_duration_seconds fields; SpeculativeEngine no longer forwards them.
inference_engine/server/metrics.py	−74	4 metrics (path_selection_total, continuation_tokens_skipped_total, verifier_prefill_duration_seconds, cache_invariant_violations_total); 2 record_* methods.
inference_engine/server/app.py	−53	_session_acceptance_rate + _emit_path_selection_metric helpers; the two call sites pass acceptance_rate=None now. The OpenAI response loses its acceptance_rate field as a side effect — acceptable on a feature-frozen deprecated shim per §2.7.
inference_engine/scheduler/session.py	−7	engine_result field on Session.
inference_engine/scheduler/scheduler.py	±3	Replaced session.engine_result = result assignment with del result.
scripts/bench_agentic/bench_long_session.py	−211/+30	All path-selection scrape logic + _adr_0007_summary + render-summary block. Module docstring points at PR-E1's bench_session_long_run.py for the replacement bench.

Files (tests)

File	Δ	What was removed
tests/inference_engine/server/test_metrics.py	−107	4 entries from test_build_registers_all_documented_metrics's expected set; 9 tests in the "ADR 0007 §2.10 — path_selection observability" section.
tests/inference_engine/server/test_app_metrics_and_auth.py	−98	4 tests: test_metrics_path_selection_metrics_present_on_idle_metrics_scrape, test_metrics_path_selection_recorded_after_completion, test_session_acceptance_rate_returns_none_when_result_missing_rate, test_emit_path_selection_metric_noop_when_path_unset.

Behavior changes visible to clients

• /metrics no longer exposes 4 ADR-0007-vintage metrics. They were unreachable anyway after PR-A3 removed the path_select machinery from the verifier.
• OpenAI chat-completions response no longer includes the acceptance_rate field. Migrate to the gRPC Generate stream + GetSessionInfo for richer telemetry.
• The deprecated HTTP shim still works exactly as before in every other respect; PR-D2 is what does the real SessionStore migration.

Linux verification

PYTHONPATH=.:sdks/python pytest <Linux CI gate set>
682 passed (was 695 - 13 ADR-0007-specific tests removed)
TOTAL  1660 stmts  100.00 % coverage (was 1694 - 34 dead stmts removed)

Per ADR 0008 §9

Pure deletion / cleanup on the Linux-runnable surface. Zero MLX runtime code touched. §9 last-paragraph carve-out invoked: Linux-only path. No Mac M4 report needed.

Reviewer checklist

• Every ADR-0007 metric is gone: grep -r "path_selection\|continuation_tokens_skipped\|verifier_prefill_duration\|cache_invariant_violations_total\|record_path_selection\|record_cache_invariant_violation\|_emit_path_selection_metric\|_session_acceptance_rate\|engine_result" inference_engine/ tests/ scripts/ returns only docstring / comment hits, no live code.
• §6.4 amendment correctly records the PR-D1 / PR-D2 split.
• No new test depends on the removed fields: 13 tests deleted, no replacements added (that's PR-D2's job).
• Existing 461-test integration suite still passes (now 682 after the deletions; the suite has grown since PR-D1's original spec was written, all post-A2 / post-B1-B5 additions are intact).

Next PR

PR-D2 (queued, not blocking v0.3 GA): the HTTP-shim refactor proper. /v1/chat/completions becomes a single-shot session under SessionStore; PooledVerifier retires; Deprecation / Sunset headers added. Linux-only path; §9 carve-out continues to apply.

After PR-D1 merges, PR-E1 (the integration suite + Mac M4 INV-3 determinism gate) can also start in parallel — they touch disjoint files.