Scope tool search to request tools and tighten deferred tool handling

[PenguinDOOM]

Summary

• centralize request-scoped tool classification with a shared request tool manifest
• scope tool search results to deferred tools available for the active request
• harden responses/messages serialization and prompt guidance for zero-deferred requests
• restore Anthropic request-scoped tool grouping, including virtual activate_* groups
• align ToolSearchTool with the request-scoped deferred snapshot, including virtual groups
• preserve tool_search request context across real invocation, shallow-clone, and plain-object/JSON round-trip boundaries with regression tests
• harden deferred tool handling by excluding tool_search from deferred manifests, sharing zero-deferred pruning, and opportunistically evicting stale request-scoped tool-search snapshots
• keep non-deferred built-in tools direct when default built-in grouping is enabled, so tools like vscode_askQuestions remain directly callable
• add regression coverage for request-scoped tool selection, endpoint behavior, prompt reminders, defaultIntentRequestHandler Anthropic grouping, clone-safe ToolSearchTool behavior, and built-in grouping behavior

Testing

• npm run gulp compile-extensions
• npm --prefix extensions/copilot run test:unit -- src/extension/intents/node/test/backgroundTodoEnablement.spec.ts src/extension/tools/node/test/testToolsService.ts
• .\node_modules\.bin\vitest.cmd run src/extension/prompt/node/test/defaultIntentRequestHandler.spec.ts --testNamePattern "keeps activate_vs_code_interaction in request-scoped tools for anthropic tool search requests"
• .\node_modules\.bin\vitest.cmd run src/extension/tools/node/test/toolSearchTool.spec.ts --testNamePattern "searches only deferred tools enabled for the active request"
• .\node_modules\.bin\vitest.cmd run src/extension/tools/node/test/toolSearchTool.spec.ts --testNamePattern "fails explicitly when invoke runs without request-scoped resolveInput context"
• .\node_modules\.bin\vitest.cmd run src/extension/tools/node/test/toolSearchTool.spec.ts --testNamePattern "retains request-scoped virtual activate groups during tool search candidate selection|preserves request-scoped deferred tools after resolved input is shallow-cloned|preserves request-scoped deferred tools after resolved input is JSON-round-tripped"
• .\node_modules\.bin\vitest.cmd run src/extension/tools/test/node/virtualTools/builtInToolGroupHandler.spec.ts --reporter=basic
• npx vitest run src/platform/endpoint/node/test/responsesApiToolSearch.spec.ts
• npx vitest run src/platform/endpoint/test/node/messagesApi.spec.ts
• npx vitest run src/extension/prompts/node/agent/test/agentPrompt.spec.tsx --testNamePattern "OpenAI reminder instructions"
• npm run test:unit -- src/extension/prompts/node/agent/test/agentPrompt.spec.tsx -t "tool_search reminder|hidden-model-m reminder"

Review follow-up

• Built-in grouping follow-up (fix(tool-grouping): keep non-deferred built-ins direct) was reviewed by Code-Review-subagent and approved.
• No blocking correctness issues were found in the BuiltInToolGroupHandler / VirtualToolGrouper changes.
• Only non-blocking notes remained: a possible clarifying comment around the effectively unreachable ToolCategory.Core summary branch, and a note that ToolSearch stays direct in the new test because it is categorized as Core.

Fixes #316779

[Copilot]

Pull request overview

This PR fixes tool-search deferral mismatches by introducing a request-scoped “tool manifest” that consistently classifies enabled tools as deferred vs non-deferred, then using that manifest to (1) scope tool-search results to tools actually deferred/available for the active request and (2) omit tool-search scaffolding/prompt guidance entirely when a request has zero deferred tools. This targets cases where models see tool suggestions (via tool search) that they cannot actually invoke in the current request.

Changes:

• Centralized request-scoped tool classification via createRequestToolManifest and used it across endpoint body builders and tools services.
• Tightened tool_search behavior: omit client tool_search machinery when no deferred tools exist; and enforce request-scoped context for ToolSearchTool invocation.
• Added regression tests and updated prompt snapshots to reflect conditional tool_search guidance/reminders.

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
extensions/copilot/src/platform/endpoint/test/node/messagesApi.spec.ts	Adds coverage ensuring Messages API omits tool_search scaffolding when no tools are deferred.
extensions/copilot/src/platform/endpoint/node/test/responsesApiToolSearch.spec.ts	Adds coverage ensuring Responses API omits client tool_search tool when no tools are deferred.
extensions/copilot/src/platform/endpoint/node/responsesApi.ts	Uses request-scoped manifest to gate tool search deferral and tool_search inclusion for Responses API.
extensions/copilot/src/platform/endpoint/node/messagesApi.ts	Uses request-scoped manifest + model capability gating to skip tool_search when it would be ineffective.
extensions/copilot/src/extension/tools/vscode-node/toolsService.ts	Prunes tool_search from enabled tools when the request contains zero deferred tools.
extensions/copilot/src/extension/tools/node/toolSearchTool.ts	Scopes tool search candidates to deferred tools enabled for the active request; enforces resolveInput context.
extensions/copilot/src/extension/tools/node/test/toolSearchTool.spec.ts	New unit tests for request-scoped tool search behavior and explicit failure without resolveInput context.
extensions/copilot/src/extension/tools/node/test/testToolsService.ts	Aligns test tools service with request-scoped manifest and tool_search pruning behavior.
extensions/copilot/src/extension/tools/common/requestToolManifest.ts	New shared helper to classify active tools into deferred vs non-deferred for a request.
extensions/copilot/src/extension/prompts/node/agent/toolSearchInstructions.tsx	Makes tool_search guidance conditional on endpoint support, tool_search availability, and presence of deferred tools.
extensions/copilot/src/extension/prompts/node/agent/test/agentPrompt.spec.tsx	Adds tests for OpenAI prompt reminders to omit tool_search guidance when no deferred tools exist.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-sonnet-4.6/all_tools.spec.snap	Snapshot updates reflecting conditional removal of tool_search instructions / deferred tool list.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-sonnet-4.6/all_non_edit_tools.spec.snap	Snapshot updates reflecting conditional removal of tool_search instructions / deferred tool list.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-sonnet-4.5/all_tools.spec.snap	Snapshot updates reflecting conditional removal of deferred tool list + whitespace normalization.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-sonnet-4.5/all_non_edit_tools.spec.snap	Snapshot updates reflecting conditional removal of deferred tool list + whitespace normalization.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-opus-4.6/all_tools.spec.snap	Snapshot updates reflecting conditional removal of tool_search instructions / deferred tool list.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-opus-4.6/all_non_edit_tools.spec.snap	Snapshot updates reflecting conditional removal of tool_search instructions / deferred tool list.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-opus-4.5/all_tools.spec.snap	Snapshot updates reflecting conditional removal of deferred tool list + whitespace normalization.
extensions/copilot/src/extension/prompts/node/agent/test/snapshots/agentPrompts-claude-opus-4.5/all_non_edit_tools.spec.snap	Snapshot updates reflecting conditional removal of deferred tool list + whitespace normalization.
extensions/copilot/src/extension/prompts/node/agent/openai/hiddenModelMPrompt.tsx	Makes reminder tool_search guidance conditional using the shared predicate and tool deferral service.
extensions/copilot/src/extension/prompts/node/agent/openai/gpt55BasePrompt.tsx	Makes reminder tool_search guidance conditional using the shared predicate and tool deferral service.
extensions/copilot/src/extension/prompts/node/agent/openai/gpt54Prompt.tsx	Makes reminder tool_search guidance conditional using the shared predicate and tool deferral service.
extensions/copilot/src/extension/prompts/node/agent/defaultAgentInstructions.tsx	Extends reminder props to include availableTools for request-scoped tool_search reminder logic.
extensions/copilot/src/extension/prompts/node/agent/agentPrompt.tsx	Plumbs availableTools into reminder instruction props.
extensions/copilot/src/extension/intents/node/test/backgroundTodoEnablement.spec.ts	Adds regression coverage around publishing/explicitly disabling vscode_askQuestions in agent tools.
extensions/copilot/src/extension/intents/node/agentIntent.ts	Allows vscode_askQuestions tool in agent tool set by default (subject to request tool picker overrides).

[PenguinDOOM]

I was able to confirm locally that there were no problems calling the tools with either GPT or Claude.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 28 changed files in this pull request and generated 5 comments.

[bhavyaus]

Thanks — the root cause is real and a good catch: a non-deferred tool (like askQuestions) getting pulled into a virtual group while defaultToolsGrouped + tool search are both active means it's never surfaced via tool_search_output, so the model can't call it.

I'm going to pass on this PR as the fix, though. The actual fix is basically a one-line invariant ("non-deferred tools must never be grouped"), but this PR is ~1,100 lines across 31 files of request-scoped manifests, serialization, and prompt-gating changes that go well beyond the root cause and touch experimental tool-search internals we're actively iterating on.