fix(agent): pass-2 Rust production cutover + comprehensive differential + CI gate

Production cutover (Thufir finding 1, Rust half):
- Add normalize_effort_for_databricks_v2() and anthropic_thinking_config_for_databricks_v2()
  as generated-backed production helpers for DatabricksV2 requests.
- llm.rs DatabricksV2 dispatch now routes through these helpers: OpenAiResponses and
  MlflowChatCompletions paths call normalize_effort_for_databricks_v2(); anthropic_body
  calls anthropic_thinking_config_for_databricks_v2(). The adopted F1 corrections
  (e.g. databricks-gpt-5-5: [low,medium,high]) are now enforced in real requests.
- Pure OpenAi/Databricks path retains normalize_effort_for_openai_route (unchanged).

Comprehensive Rust differential (Thufir finding 4):
- Replace the simple route-only differential test (20-vector literal list, no allowlist
  scoping) with a comprehensive multi-axis test covering all 3 input sets:
  effortTable.fixture.json (36), normative-corpus.json (45), catalog-sample-fixture.json (14).
- Axes: supported_efforts, default_effort, databricks_v2_wire_route, thinking_mode.
- Allowlist is axis-scoped; 7 entries, all doc-cited. Stale entries FAIL (mirrors JS
  harness semantics — no whole-record skip).
- Exposes strip_catalog_prefix as pub(crate); adds #[cfg(test)] pub(crate) helpers
  is_manual_budget_model_for_test, is_adaptive_thinking_model_for_test, and
  valid_effort_values_for_provider_model_for_test so llm.rs tests can call
  config.rs classifiers without duplicating them.
- Result: 95 input entries, 7/7 allowlist slots exercised, 0 unexpected divergences.

CI gate (Thufir finding 3):
- Extend model-capability-regen-diff workflow path filter to cover the differential
  harness, all three fixtures, and both old/new consumer files (buzzAgentConfig.ts,
  config.rs, llm.rs) so any change to either side triggers the gate.
- Add a final step: node --experimental-strip-types scripts/run-differential.mjs.

Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

.github/workflows/model-capability-regen-diff.yml

@@ -9,6 +9,14 @@ on:
       - 'desktop/src/features/agents/ui/modelCapabilities.ts'
       - 'scripts/generated-model-capabilities-coverage.json'
       - '.github/workflows/model-capability-regen-diff.yml'
+      # Differential harness and fixtures — any change to old/new side or inputs re-runs.
+      - 'scripts/run-differential.mjs'
+      - 'scripts/normative-corpus.json'
+      - 'scripts/catalog-sample-fixture.json'
+      - 'desktop/src/features/agents/ui/effortTable.fixture.json'
+      - 'desktop/src/features/agents/ui/buzzAgentConfig.ts'
+      - 'crates/buzz-agent/src/config.rs'
+      - 'crates/buzz-agent/src/llm.rs'
   push:
     branches: [main, release, 'duncan/databricks-model-label-registry']
 
@@ -51,3 +59,6 @@ jobs:
 
       - name: Validate manifest (schema-negative tests)
         run: node --test scripts/test-manifest-validator.mjs
+
+      - name: Run differential harness (old vs new, all input sets)
+        run: node --experimental-strip-types scripts/run-differential.mjs