fix(web): disambiguate MCP language model selection for ask_codebase

[Harsh23Kashyap]

Fixes #1137

Summary

• match askCodebase requests by provider and model before considering displayName
• require displayName only when multiple configured models share the same provider and model
• add focused unit coverage for the selection and disambiguation cases

Test plan

• yarn workspace @sourcebot/web test --run "src/ee/features/mcp/askCodebase.test.ts"
• yarn workspace @sourcebot/web lint "src/ee/features/mcp/askCodebase.ts" "src/ee/features/mcp/askCodebase.test.ts"
• ReadLints clean for the touched files
• local Yarn commands could not run here because the repo is missing the Yarn install state (node_modules state file)

Summary by CodeRabbit

• Bug Fixes
  • Improved language model selection so the app now matches configured models by provider and model, and only asks for a display name when needed to tell similar entries apart.
  • Added clearer error handling when no matching model is found or when the chosen name doesn’t exist.
• Tests
  • Added coverage for model selection, duplicate-model disambiguation, and invalid request cases.
• Documentation
  • Updated the changelog with the latest fix.

[coderabbitai]

Walkthrough

This PR fixes MCP ask_codebase language model selection by adding selectConfiguredLanguageModel, which matches configured models on provider+model and only requires displayName for disambiguation when multiple configured entries share that pair, replacing the previous key-based match that incorrectly required displayName always. Tests and a changelog entry are added.

Changes

Language model selection fix

Layer / File(s)	Summary
selectConfiguredLanguageModel helper and type packages/web/src/ee/features/mcp/askCodebase.ts	Adds a ConfiguredLanguageModel type and the selectConfiguredLanguageModel function matching by provider+model, disambiguating via displayName, and returning ServiceError for no match, wrong displayName, or unresolved multiple matches; removes unused getLanguageModelKey import.
Wire selection helper into askCodebase packages/web/src/ee/features/mcp/askCodebase.ts	Replaces the previous inline getLanguageModelKey-based matching with a call to selectConfiguredLanguageModel, propagating its ServiceError or returning an internal error if no config is unexpectedly resolved.
Selection helper tests and changelog packages/web/src/ee/features/mcp/askCodebase.test.ts, CHANGELOG.md	Adds a Vitest suite covering successful selection, displayName disambiguation, and BAD_REQUEST/INVALID_REQUEST_BODY error cases, plus a changelog entry describing the fix.

Estimated code review effort: 2 (Simple) | ~15 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant askCodebase
  participant selectConfiguredLanguageModel

  Client->>askCodebase: request with languageModel (provider, model)
  askCodebase->>selectConfiguredLanguageModel: configuredModels, requestedLanguageModel
  alt no match
    selectConfiguredLanguageModel-->>askCodebase: ServiceError (not configured)
  else displayName mismatch
    selectConfiguredLanguageModel-->>askCodebase: ServiceError (wrong displayName)
  else multiple matches, no displayName
    selectConfiguredLanguageModel-->>askCodebase: ServiceError (ambiguous, need displayName)
  else single match
    selectConfiguredLanguageModel-->>askCodebase: languageModelConfig
  end
  askCodebase-->>Client: ServiceError or selected config

Loading

Possibly related PRs

• sourcebot-dev/sourcebot#1018: Also changes ask_codebase behavior around configured language models, in the MCP tool registration path.
• sourcebot-dev/sourcebot#1370: Also modifies askCodebase.ts, using the selected languageModelConfig to resolve contextWindow.
• sourcebot-dev/sourcebot#1372: Also depends on askCodebase's languageModelConfig selection to populate capability fields on the response payload.

Suggested reviewers: jsourcebot

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: fixing ask_codebase language model selection disambiguation.
Linked Issues check	✅ Passed	The code matches provider/model first, uses displayName only to break ties, preserves default selection, and adds tests for the reported cases.
Out of Scope Changes check	✅ Passed	The diff stays focused on the model-selection fix, related tests, and a changelog note with no unrelated feature work.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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🧹 Nitpick comments (1)

packages/web/src/ee/features/mcp/askCodebase.test.ts (1)

19-85: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Missing test for the "not configured" (zero candidates) branch.

The suite covers omitted-displayName match, displayName disambiguation, multiple-match error, and displayName-mismatch error, but doesn't test the case where no configured model matches provider+model at all (candidateModels.length === 0 branch in selectConfiguredLanguageModel, packages/web/src/ee/features/mcp/askCodebase.ts Lines 56-64).

✅ Suggested additional test

+    it("returns an error when no configured model matches provider and model", () => {
+        const configuredModel = createConfiguredModel();
+
+        const result = selectConfiguredLanguageModel(
+            [configuredModel],
+            { provider: 'openai', model: 'gpt-5' }
+        );
+
+        expect(result).toEqual({
+            error: {
+                statusCode: StatusCodes.BAD_REQUEST,
+                errorCode: ErrorCode.INVALID_REQUEST_BODY,
+                message: "Language model 'openai/gpt-5' is not configured.",
+            },
+        });
+    });

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@packages/web/src/ee/features/mcp/askCodebase.test.ts` around lines 19 - 85,
Add a test in selectConfiguredLanguageModel’s describe block to cover the
zero-candidate branch where no configured model matches the requested
provider/model. Use createConfiguredModel with a non-matching provider or model,
call selectConfiguredLanguageModel with that request, and assert it returns the
expected not-configured error shape rather than a languageModelConfig. This
should sit alongside the existing cases for disambiguation and displayName
mismatch so the candidateModels.length === 0 path is covered.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@packages/web/src/ee/features/mcp/askCodebase.test.ts`:
- Around line 19-85: Add a test in selectConfiguredLanguageModel’s describe
block to cover the zero-candidate branch where no configured model matches the
requested provider/model. Use createConfiguredModel with a non-matching provider
or model, call selectConfiguredLanguageModel with that request, and assert it
returns the expected not-configured error shape rather than a
languageModelConfig. This should sit alongside the existing cases for
disambiguation and displayName mismatch so the candidateModels.length === 0 path
is covered.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f43ad8e7-f916-49f8-a763-7d2b548aa79c

📥 Commits

Reviewing files that changed from the base of the PR and between fd6720f and 72b615d.

📒 Files selected for processing (3)

• CHANGELOG.md
• packages/web/src/ee/features/mcp/askCodebase.test.ts
• packages/web/src/ee/features/mcp/askCodebase.ts