Coherence pass — PRD/PHASES updates, config snapshot wired, unit tests

J flagged the audit: "make sure everything flows coherently, no
pseudocode or unnecessary patches or ignoring any particular part of
what we built." This is that pass.

PRD.md updates:
- Phase 19 refinement block — geo-filter + role-prefilter WIRED with
  citation density numbers (0.32 → 1.38, and 2 → 28 on same scenario).
- Phase 20 rewrite — mistral dropped, qwen3.5 + qwen3 local hot path,
  think:false as the key mechanical finding, kimi-k2.6 upgrade path.
- Phase 21 status block — think plumbing + cloud executor routing
  added after original commit.
- Phase 22 item B (cloud rescue) — pivot sanitizer, rescue verified
  1/3 on stress_01.
- Phase 23 NEW — staffer identity + tool_level + competence-weighted
  retrieval + kb_staffer_report. Auto-discovered worker labels called
  out with real numbers (Rachel Lewis 12× across 4 staffers).
- Phase 24 NEW — Observer/Autotune integration gap DOCUMENTED, not
  fixed. Observer has been idle at 0 ops for 3600+ cycles because
  scenarios hit gateway:3100 directly, bypassing MCP:3700 which the
  observer wraps. This is the honest "we're not using it in these
  tests" signal J surfaced. Fix deferred; gap visible now.

PHASES.md:
- Appended Phases 20-23 as checked, Phase 24 as unchecked gap.
- Updated footer count: 102 unit tests across all layers.
- Latest line updated with 14× citation lift + 46.4pt tool-asymmetry
  finding.

scenario.ts:
- snapshotConfig() was defined but never called. Now fires at every
  scenario start with a stable sha256 hash over the active model set +
  tool_level + cloud flags. config_snapshots.jsonl finally populates,
  which the error_corrections diff path needs to work correctly.

kb.test.ts (new): 4 signature invariant tests — stability across
unrelated fields (date, contract, staffer), sensitivity to role/city/
count changes, digest shape. All pass under `bun test`.

service.rs: 6 Rust extractor tests for extract_target_geo +
extract_target_role — basic, missing-state-returns-none, word
boundary (civilian != city), multi-word role, absent role, quoted
value parse. All pass under `cargo test -p vectord --lib extractor_tests`.

Dangling items now honestly documented rather than silently pending:
- Chunking cache (config/models.json SPEC, not wired) — flagged
- Playbook versioning (SPEC, not wired) — flagged
- Observer integration (WIRED but disconnected) — new Phase 24

tests/multi-agent/scenario.ts

@@ -35,7 +35,8 @@ import {
   reviewerPrompt,
   GATEWAY,
 } from "./agent.ts";
-import { indexRun, recommendFor, loadRecommendation, type PathwayRecommendation } from "./kb.ts";
+import { indexRun, recommendFor, loadRecommendation, snapshotConfig, type PathwayRecommendation } from "./kb.ts";
+import { createHash } from "node:crypto";
 import { mkdir, writeFile, appendFile } from "node:fs/promises";
 import { join } from "node:path";
 
@@ -1450,6 +1451,35 @@ async function main() {
   // per run. If no staffer or no tool_level, defaults hold.
   applyToolLevel(spec.staffer?.tool_level);
 
+  // Phase 22 — record the config snapshot each run gets. Lets the
+  // error_corrections detector diff configs between fail→succeed pairs
+  // and gives the KB a receipt of what was active for any given
+  // outcome. Hash computed over the active model set + tool_level so
+  // the same staffer running back-to-back with no config change
+  // doesn't clutter the file.
+  try {
+    const activeModels = {
+      executor: ACTIVE_EXECUTOR,
+      reviewer: ACTIVE_REVIEWER,
+      overview: OVERVIEW_MODEL,
+      executor_cloud: String(ACTIVE_EXECUTOR_CLOUD),
+      overview_cloud: String(ACTIVE_OVERVIEW_CLOUD),
+      t3_disabled: String(ACTIVE_T3_DISABLED),
+      tool_level: spec.staffer?.tool_level ?? "default",
+    };
+    const configHash = createHash("sha256")
+      .update(JSON.stringify(activeModels))
+      .digest("hex")
+      .slice(0, 16);
+    await snapshotConfig(
+      configHash,
+      activeModels,
+      `scenario_start ${spec.client} ${spec.date} staffer=${spec.staffer?.id ?? "none"}`,
+    );
+  } catch (e) {
+    console.log(`   (config snapshot skipped: ${(e as Error).message})`);
+  }
+
   console.log(`▶ scenario: ${spec.client}, ${spec.date}, ${spec.events.length} events`);
   if (spec.staffer) {
     const level = spec.staffer.tool_level ?? "(default)";