feat(agent): Phase 2 — wire Rust and TS consumers to generated model-capabilities module (#3958)

## What

Phase 2 consumer cutover targeting the
`duncan/databricks-model-label-registry` umbrella branch. Wires
`crates/**` and `desktop/**` consumers to the generated capability
module introduced in Phase 1 (#3821), while keeping old and new paths
both live for differential testing. Phase 3 removes the old paths.

## Commits (boundary-separated)

### feat(agent): Phase 2a — wire Rust consumers to generated capability
module (`crates/**`, `scripts/**`)

- `catalog.rs`: `DATABRICKS_V2_KNOWN_MODELS` re-exported from the
generated module — single source of truth.
- `llm.rs`: `databricks_v2_route_for_model` delegates to
`resolve_model_capabilities("databricks_v2", model)`. Old segment-based
classifier preserved as `#[cfg(test)] _old_*` for the differential
harness. New `databricks_v2_route_differential_old_vs_new` test confirms
100% agreement on all 20 route vectors.
- `config.rs`: new `effort_table_fixture_differential_old_vs_new` test
runs `resolve_model_capabilities` over the 36-entry
`effortTable.fixture.json` and asserts old/new agree modulo a doc-cited
allowlist (4 F1 corrections).
- `scripts/run-differential.mjs`: JS differential harness over
effortTable fixture + normative corpus + catalog-sample fixture. 85
checks, 0 unexpected divergences (5 allowlisted: 4 F1 corrections +
goose-opus-5 anthropic route correction).
- `scripts/MODELS_DEV_RECONCILIATION.md`: deferred MINOR from Phase 1 —
8 trailing-double-space line breaks replaced with `<br>`.

### feat(desktop): Phase 2b — cut TS consumers to generated
model-capabilities module (`desktop/**`)

- `buzzAgentConfig.ts`: adds
`getProviderEffortConfigFromManifest(provider, model?)` — thin wrapper
over `resolveModelCapabilities()` from `modelCapabilities.ts`. Maps
`supportedEfforts → validValues` and `defaultEffort → defaultValue`
(null preserved for manual-budget/Inherit). Old
`getProviderEffortConfig()` and all hand-tables stay live for the
differential harness; Phase 3 retires them.
- `formatAgentModelLabel.ts`: registry-label lookup re-pointed from
hand-maintained `databricksModelNames.ts` import to generated
`DATABRICKS_MODEL_NAMES` exported from `modelCapabilities.ts`. Same Map
shape, identical contents, behavior unchanged.

### fix(scripts): add ts-esm-loader and fix allowlist coverage in
run-differential (`scripts/**`)

- `scripts/ts-esm-loader.mjs`: minimal ESM custom loader that resolves
extensionless relative TS imports. Required because Phase 2b's
`buzzAgentConfig.ts` imports `modelCapabilities` without `.ts` extension
— which Node's `--experimental-strip-types` runner cannot resolve
without a hook.
- `scripts/run-differential.mjs`: shebang updated to self-bootstrap with
the loader; fixes the `totalAllowlisted` counter (was declared but never
incremented — always printed `0 allowlisted`). Replaced with per-axis
hit tracking: reports exercised slot count (`N/total`) in summary; fails
with `STALE_ALLOWLIST` if any declared entry fires zero divergences,
preventing stale entries from silently masking future regressions.

## Verification

- `cargo test -p buzz-agent --lib`: 426/426
- Corpus: 45/45 · schema-negative: 24/24 · `--check` byte-clean
- Differential: 85 checks, 0 unexpected divergences, 6/6 allowlist slots
exercised
- Desktop: 3847/3847 · typecheck clean · biome clean
- Mobile: 1019 pass, 1 skipped — same 5 flaky tests in
`mobile/test/features/channels/` that reproduce at the umbrella base;
zero mobile files in this branch range
- `git diff --check`: clean

## What Remains (Phase 3)

Remove old hand-maintained paths: `_old_*` functions in
`llm.rs`/`config.rs`, old `getProviderEffortConfig` tables in
`buzzAgentConfig.ts`, old `databricksModelNames.ts` import in
`formatAgentModelLabel.ts`, old `databricks_model_names.rs` module.

---------

Signed-off-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: npub1g8493u0xfsjrvflg4n08ezd7vec99mnwzlv0qgwpr9d7gvjwhuzqx59rhw <41ea58f1e64c243627e8acde7c89be667052ee6e17d8f021c1195be4324ebf04@buzz.block.builderlab.xyz>
Signed-off-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@buzz.block.builderlab.xyz>
Co-authored-by: npub1mn7jgtj4w2pd0g0zeuhxsa6jy6p0rewxz4kujt98my82ahfmp72sxjexk7 <dcfd242e557282d7a1e2cf2e6877522682f1e5c6156dc92ca7d90eaedd3b0f95@buzz.block.builderlab.xyz>
Co-authored-by: npub1g8493u0xfsjrvflg4n08ezd7vec99mnwzlv0qgwpr9d7gvjwhuzqx59rhw <41ea58f1e64c243627e8acde7c89be667052ee6e17d8f021c1195be4324ebf04@buzz.block.builderlab.xyz>

.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 +59,19 @@ 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
+
+  rust-unit-tests:
+    name: buzz-agent unit tests (normative corpus + behavioral differential)
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: read
+
+    steps:
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+
+      - name: Run buzz-agent unit tests
+        run: cargo test -p buzz-agent --lib