feat: Auto-exclude built-in tools overridden by user-registered tools

[Copilot]

When users register tools whose names collide with CLI built-ins (e.g. edit_file, read_file), the CLI would intercept those calls instead of dispatching to the user's handler. The fix: automatically merge user-registered tool names into excludedTools on session.create/session.resume, so the CLI skips its built-in and the SDK dispatches locally.

Changes

• Node.js — mergeExcludedTools() helper; applied in createSession + resumeSession
• Python — inline merge using dict.fromkeys() for dedup; applied in create_session + resume_session
• Go — mergeExcludedTools() helper with map-based dedup; applied in CreateSession + ResumeSessionWithOptions
• .NET — MergeExcludedTools() internal static helper using Union(); applied in CreateSessionAsync + ResumeSessionAsync; added InternalsVisibleTo for test project
• Tests — unit tests in all 4 SDKs covering: names added, deduplication, no-op (no tools), and resume path
• Docs — "Overriding Built-in Tools" subsection added to all 4 READMEs

Example (Node.js)

// Register a tool named after a CLI built-in — your handler is called instead
const session = await client.createSession({
  tools: [defineTool("edit_file", {
    description: "Custom editor with project-specific validation",
    parameters: z.object({ path: z.string(), content: z.string() }),
    handler: async ({ path, content }) => { /* your logic */ },
  })],
  // No need to manually add "edit_file" to excludedTools — SDK does it automatically
});

Backward-compatible: users with no name collisions see no behavior change.

Warning

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Original prompt

i want to review the code in this branch

Chronological Review: 1. User asked about branch changes → on main, no changes 2. User asked for 10 recent issues → listed, recommended #518 3. User asked to find issue about overriding tools → found #411 4. User entered plan mode → analyzed codebase extensively via explore agents, created plan with 5 todos 5. User entered fleet mode → dispatched 4 parallel agents for SDK implementations 6. All 4 agents completed, then docs agent dispatched and completed 7. User asked to commit, push, and open PR → done successfully

Intent Mapping:

• Find branch changes
• Review recent issues
• Find tool override issue (Support overriding built-in tools #411)
• Plan implementation
• Execute plan across all 4 SDKs
• Commit, push, and open PR

Technical Inventory:

• github/copilot-sdk repo with 4 SDKs: Node.js, Python, Go, .NET
• Issue Support overriding built-in tools #411: Support overriding built-in tools
• Solution: auto-add user tool names to excludedTools in RPC payload
• mergeExcludedTools helper pattern across SDKs

Code changes across 13 files, all committed and pushed.

Recent Commands: git commit, git push, gh pr create → PR #522 created

1. Conversation Overview: - Primary Objectives: User wanted to explore the copilot-sdk repo, find a good issue to work on, then plan and implement Issue #411 ("Support overriding built-in tools"), and finally commit/push/open a PR. - Session Context: Started with repo exploration → issue review → found #411 about tool overrides → planned implementation → executed across all 4 SDKs in parallel → committed and opened PR #522. - User Intent Evolution: Browse issues → focus on #411 → plan → execute → ship.

2. Technical Foundation:

   • Repo: github/copilot-sdk at /Users/patrick/projects/copilot-sdk
   • 4 SDKs: Node.js (nodejs/), Python (python/), Go (go/), .NET (dotnet/)
   • Issue Support overriding built-in tools #411: Users registering tools with names colliding with built-in CLI tools (e.g., Bash, Read, Edit) couldn't override them — CLI handled them instead of dispatching to user's handler.
   • Solution: Auto-add user-registered tool names to excludedTools in the session.create/session.resume RPC payload so CLI excludes its built-in and SDK dispatches locally.
   • Key architecture: SessionConfig.tools → mapped to RPC payload → CLI uses excludedTools to skip built-ins → SDK's tool.call handler dispatches to user's registered handler.

3. Codebase Status:

   • nodejs/src/client.ts:
     • Added mergeExcludedTools() helper function (~L57)
     • Called in createSession (~L545) and resumeSession (~L623)
   • nodejs/test/client.test.ts:
     • 4 new tests: tools added to excludedTools, deduplication, no-op, resumeSession
   • python/copilot/client.py:
     • Inline merge logic in both create_session (~L483) and resume_session (~L658)
     • Uses dict.fromkeys() for deduplication
   • python/test_client.py:
     • 4 new tests in TestExcludedToolsFromRegisteredTools class; all 26 tests pass
   • go/client.go:
     • Added mergeExcludedTools() helper (~L1355)
     • Called in CreateSession (~L464) and ResumeSessionWithOptions (~L561)
   • go/client_test.go:
     • TestMergeExcludedTools with 4 sub-tests
   • dotnet/src/Client.cs:
     • Added MergeExcludedTools() internal static helper (~L855)
     • Called in CreateSessionAsync (~L385) and ResumeSessionAsync (~L470)
   • dotnet/src/GitHub.Copilot.SDK.csproj:
     • Added InternalsVisibleTo for test project
   • dotnet/test/MergeExcludedToolsTests.cs:
     • New file with 5 tests; all pass
   • All 4 READMEs updated with "Overriding Built-in Tools" subsection + code examples

4. Problem Resolution:

   • Issue Support overriding built-in tools #411 comments confirmed: maintainer @SteveSandersonMS approved "override by name" approach
   • No externalToolDefinitions/externalToolDispatcher fields exist despite issue description — the SessionConfig.tools + excludedTools approach is the correct mechanism
   • Backward-compatible: users not naming tools after built-ins see no change

5. Progress Tracking:

   • ✅ node-override — done
   • ✅ python-override — done
   • ✅ go-override — done
   • ✅ dotnet-override — done
   • ✅ docs-update — done
   • ✅ Committed, pushed, PR opened

6. Active Work State:

   • All work complete. PR feat: Support overriding built-in tools #522 is open at feat: Support overriding built-in tools #522
   • Branch: support-tool-overrides
   • 13 files changed, 395 insertions, 9 deletions

7. Recent Operations:

   • Last Agent Commands:
     1. git checkout -b support-tool-overrides && git add -A → branch created, all changes staged
     2. git commit -m "feat: auto-exclude built-in tools overridden by user-registered tools..." → committed as dc83960
     3. git push -u origin support-tool-overrides → pushed successfully
     4. gh pr create --title "feat: Support overriding built-in tools" --body "..." --base main → created PR feat: Support overriding built-in tools #522
   • Tool Results Summary: All succeeded. PR URL: https://github.com/git...

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