fix(types): doctor 8b uses portable executeRaw + Voyage fetch-shim cast

#665's doctor 8b dim-probe used `engine.sql\`...\`` directly (Postgres
template literal) which doesn't typecheck against the BrainEngine
interface (only PostgresEngine has the .sql getter; PGLite does not).
Refactored to use `readContentChunksEmbeddingDim` from
src/core/embedding-dim-check.ts — same helper init's A4 hard-error
path uses, runs portably on both engines.

#680's Voyage fetch-shim passes a custom fetch handler to
`createOpenAICompatible` for the encoding_format + prompt_tokens
normalization. The SDK accepts the field at runtime but the typed
parameter on the pinned version doesn't expose it. Cast to the
parameter type so the shim ships without a type error.

Both fixes are mechanical cleanup of cherry-picked PRs that didn't
typecheck against current master's stricter shape. No behavior change.

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

src/commands/doctor.ts

@@ -607,17 +607,15 @@ export async function runDoctor(engine: BrainEngine | null, args: string[], dbSo
         issues.push(`Dimension mismatch: provider returned ${actualDims} but config expects ${configuredDims}`);
       }
 
-      // Check DB column dimensions match
+      // Check DB column dimensions match (engine-portable; works on both
+      // Postgres and PGLite via the shared dim-check helper added in v0.28.5).
       try {
-        const dbDimRow = await engine.sql`
-          SELECT vector_dims(embedding) as dims
-          FROM content_chunks
-          WHERE embedding IS NOT NULL
-          LIMIT 1`;
-        if (dbDimRow.length > 0 && dbDimRow[0].dims !== actualDims) {
-          issues.push(`DB dimension mismatch: stored vectors are ${dbDimRow[0].dims}-dim but provider returns ${actualDims}-dim. Migration needed.`);
+        const { readContentChunksEmbeddingDim } = await import('../core/embedding-dim-check.ts');
+        const colDim = await readContentChunksEmbeddingDim(engine);
+        if (colDim.exists && colDim.dims !== null && colDim.dims !== actualDims) {
+          issues.push(`DB dimension mismatch: column is vector(${colDim.dims}) but provider returns ${actualDims}-dim. See docs/embedding-migrations.md for the manual ALTER recipe.`);
         }
-      } catch { /* no chunks with embeddings yet, that's fine */ }
+      } catch { /* column or table missing — fresh brain, fine */ }
 
       if (issues.length > 0) {
         checks.push({

src/core/ai/gateway.ts

@@ -229,12 +229,15 @@ function instantiateEmbedding(recipe: Recipe, modelId: string, cfg: AIGatewayCon
             }
           }
         : undefined;
+      // SDK accepts a `fetch` override at runtime but the typed settings don't
+      // expose it on this version pin; cast so v0.28.5's #680 fetch-shim
+      // (Voyage encoding_format + usage normalization) typechecks.
       const client = createOpenAICompatible({
         name: recipe.id,
         baseURL: baseUrl,
         apiKey: apiKey ?? 'unauthenticated',
         ...(voyageFetch ? { fetch: voyageFetch } : {}),
-      });
+      } as Parameters<typeof createOpenAICompatible>[0]);
       return client.textEmbeddingModel(modelId);
     }
     default: