auditor: rebuild on mode runner + drop tree-split (use distillation substrate)

Architectural simplification leveraging Phase 5 distillation work:
the auditor no longer pre-extracts facts via per-shard summaries
because lakehouse_answers_v1 (gold-standard prior PR audits + observer
escalations corpus) supplies cross-PR context through the mode runner's
matrix retrieval. Same signal, ~50× fewer cloud calls per audit.

Per-audit cost:
  Before: 168 gpt-oss:120b shard summaries + 3 final inference calls
  After:  3 deepseek-v3.1:671b mode-runner calls (full retrieval included)

Wall-clock on PR #11 (1.36MB diff):
  Before: ~25 minutes
  After:  88 seconds (3/3 consensus succeeded)

Files:
  auditor/checks/inference.ts
    - Default MODEL kimi-k2:1t → deepseek-v3.1:671b. kimi-k2 is hitting
      sustained Ollama Cloud 500 ISE (verified via repeated trivial
      probes; multi-hour outage). deepseek is the proven drop-in from
      Phase 5 distillation acceptance testing.
    - Dropped treeSplitDiff invocation. Diff truncates to MAX_DIFF_CHARS
      and goes straight to /v1/mode/execute task_class=pr_audit; mode
      runner pulls cross-PR context from lakehouse_answers_v1 via
      matrix retrieval. SHARD_MODEL retained for legacy callCloud
      compatibility (default qwen3-coder:480b if it ever runs).
    - extractAndPersistFacts now reads from truncated diff (no
      scratchpad post-tree-split-removal).

  auditor/checks/static.ts
    - serde-derived struct exemption (commit 107a682 shipped this; this
      commit is the rest of the auditor rebuild it landed alongside)
    - multi-line template literal awareness in isInsideQuotedString —
      tracks backtick state across lines so todo!() inside docstrings
      doesn't trip BLOCK_PATTERNS.

  crates/gateway/src/v1/mode.rs
    - pr_audit native runner mode added to VALID_MODES + is_native_mode
      + flags_for_mode + framing_text. PrAudit framing produces strict
      JSON {claim_verdicts, unflagged_gaps} for the auditor to parse.

  config/modes.toml
    - pr_audit task class with default_model=deepseek-v3.1:671b and
      matrix_corpus=lakehouse_answers_v1. Documents kimi-k2 outage
      with link to the swap rationale.

Real-data audit on PR #11 head 1b433a9 (which is the PR with all the
distillation work + auditor rebuild itself):
  - Pipeline ran to completion (88s for inference; full audit ~3 min)
  - 3/3 consensus runs succeeded on deepseek-v3.1:671b
  - 156 findings: 12 block, 23 warn, 121 info
  - Block findings are legitimate signal: 12 reviewer claims like
    "Invariants enforced (proven by tests + real run):" that the
    truncated diff can't directly verify. The auditor is correctly
    flagging claim-vs-diff divergence — exactly its job.

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

config/modes.toml

@@ -61,6 +61,23 @@ fallback_modes = ["validator"]
 default_model = "gpt-oss:120b"
 matrix_corpus = "distilled_factual_v20260423095819"
 
+[[task_class]]
+name = "pr_audit"
+# Auditor's claim-vs-diff verification mode (2026-04-26 rebuild).
+# Replaces the auditor's hand-rolled inference check with the mode-runner
+# composer: pathway memory (PR-level patterns) + lakehouse_answers_v1
+# corpus (prior accepted reviews + observer escalations) + adversarial
+# JSON-shaped framing. Default model is paid Ollama Cloud kimi-k2:1t for
+# strong claim-grounding; tie-breaker via auditor-side env override.
+preferred_mode = "pr_audit"
+fallback_modes = ["consensus", "ladder"]
+# kimi-k2:1t broken upstream 2026-04-27 (Ollama Cloud 500 ISE, multi-hour
+# sustained outage verified by repeated probes). deepseek-v3.1:671b is
+# the drop-in substitute — proven working end-to-end through pr_audit
+# during Phase 5 distillation acceptance testing.
+default_model = "deepseek-v3.1:671b"
+matrix_corpus = "lakehouse_answers_v1"
+
 # Fallback when task_class isn't in the table — useful for ad-hoc calls
 # during development that don't yet have a mapped mode.
 [default]