Add preMcpToolCall hook support to all SDKs

[stephentoub]

Motivation

The copilot-agent-runtime 1.0.51 added a new preMcpToolCall hook that lets SDK consumers intercept MCP tool invocations before they execute -- specifically to inspect, set, replace, or remove the _meta field sent to the MCP server. This PR adds support for that hook across all five language SDKs.

Approach

Each SDK receives a new hook callback (OnPreMcpToolCall / on_pre_mcp_tool_call) that is invoked with contextual information about the pending MCP tool call (server name, tool name, arguments, working directory, timestamp, existing meta). The hook returns a tri-state output:

• Return null/None -- preserve the existing _meta unchanged
• Return output with metaToUse set to an object -- replace _meta with that object
• Return output with metaToUse set to null/None -- remove _meta entirely

Key design decisions

• Wire format uses "cwd" but the public SDK API exposes it as WorkingDirectory/working_directory for consistency with the rest of the SDK surface. All existing hook input types were renamed from Cwd to WorkingDirectory as well (with serialization attributes preserving the wire name).
• .NET uses a SerializeHookOutput helper to pre-serialize the typed output to JsonElement before boxing into the generic HooksInvokeResponse(object? Output) -- required because reflection-based serialization is disabled in the project.
• The hasHooks checks in .NET and Go were updated to include OnPreMcpToolCall so the runtime knows to invoke hooks.

Testing

• E2E tests added for all 5 SDKs (15 new tests total), covering all three meta manipulation scenarios (set, replace, remove)
• Tests use a shared MCP "meta-echo" server (test/harness/test-mcp-meta-echo-server.mjs) that echoes back the _meta it received in the tool result
• Three new snapshot YAML files in test/snapshots/pre_mcp_tool_call_hook/
• .NET serialization unit tests verifying correct JSON output for all hook return shapes
• All tests pass locally across .NET, Node.js, Go, Python, and Rust

Files of note

• test/harness/test-mcp-meta-echo-server.mjs -- shared MCP server for E2E tests
• dotnet/src/Types.cs -- PreMcpToolCallHookInput and PreMcpToolCallHookOutput types
• rust/src/hooks.rs -- Rust hook trait extension and dispatch logic
• test/harness/replayingCapiProxy.ts -- minor fix to forward hook RPC calls correctly

[Copilot]

Pull request overview

Adds cross-SDK support for the new preMcpToolCall runtime hook so consumers can inspect/modify/remove MCP request _meta before tool dispatch, and updates hook payload APIs to expose WorkingDirectory/workingDirectory while preserving the on-the-wire "cwd" key.

Changes:

• Introduces preMcpToolCall hook handlers and input/output types across Rust, .NET, Go, Node.js, and Python (including runtime dispatch/handler registration).
• Renames existing hook input cwd fields to WorkingDirectory/workingDirectory (with wire-format mapping back to "cwd").
• Adds shared MCP “meta-echo” test server + snapshot-driven E2E tests for set/replace/remove-meta scenarios; adds .NET serialization tests for hook output shapes.

Show a summary per file

File	Description
test/snapshots/pre_mcp_tool_call_hook/should_set_meta_via_premcptoolcall_hook.yaml	New replay snapshot for “set meta” scenario.
test/snapshots/pre_mcp_tool_call_hook/should_replace_meta_via_premcptoolcall_hook.yaml	New replay snapshot for “replace meta” scenario.
test/snapshots/pre_mcp_tool_call_hook/should_remove_meta_via_premcptoolcall_hook.yaml	New replay snapshot for “remove meta” scenario.
test/harness/test-mcp-meta-echo-server.mjs	Adds MCP stdio server that echoes received _meta for E2E validation.
test/harness/replayingCapiProxy.ts	Adds optional debug logging to help diagnose snapshot prefix mismatches.
rust/tests/e2e/support.rs	Removes now-unneeded dead_code suppression for repo_root().
rust/tests/e2e/pre_mcp_tool_call_hook.rs	Adds Rust E2E tests covering set/replace/remove meta via hook.
rust/tests/e2e/hooks_extended.rs	Updates tests to assert working_directory instead of cwd.
rust/tests/e2e.rs	Registers new Rust E2E module.
rust/src/hooks.rs	Adds PreMcpToolCall hook types + dispatch; renames hook cwd fields to working_directory (wire "cwd").
rust/examples/hooks.rs	Updates example to use working_directory.
python/e2e/test_pre_mcp_tool_call_hook_e2e.py	Adds Python E2E tests for preMcpToolCall meta manipulation.
python/e2e/test_hooks_extended_e2e.py	Updates extended hook test to expect workingDirectory.
python/copilot/session.py	Adds new hook TypedDicts/handler type and dispatch wiring; remaps "cwd" to workingDirectory for hook inputs.
nodejs/test/e2e/pre_mcp_tool_call_hook.e2e.test.ts	Adds Node E2E tests for preMcpToolCall meta manipulation.
nodejs/test/e2e/hooks_extended.e2e.test.ts	Updates extended hook test assertions to use workingDirectory.
nodejs/src/types.ts	Adds new PreMcpToolCall* types and hook registration; renames hook base input cwd to workingDirectory.
nodejs/src/session.ts	Remaps raw hook input { cwd } to { workingDirectory } during deserialization.
go/types.go	Adds Go PreMcpToolCall hook types + meta tri-state helpers; renames several public Cwd-named fields to WorkingDirectory (wire "cwd").
go/session.go	Wires preMcpToolCall into hook invoke dispatcher.
go/internal/e2e/session_e2e_test.go	Updates assertions to use Context.WorkingDirectory.
go/internal/e2e/pre_mcp_tool_call_hook_e2e_test.go	Adds Go E2E tests for meta set/replace/remove via hook.
go/internal/e2e/mcp_and_agents_e2e_test.go	Updates MCP stdio config field to WorkingDirectory.
go/internal/e2e/hooks_extended_e2e_test.go	Updates hook extended test to use WorkingDirectory.
go/internal/e2e/client_options_e2e_test.go	Updates captured CLI JSON struct to WorkingDirectory field (wire "cwd").
go/client.go	Updates hasHooks detection to include OnPreMcpToolCall.
dotnet/test/Unit/SerializationTests.cs	Adds unit tests validating serialization shapes for PreMcpToolCallHookOutput and boxed JsonElement outputs.
dotnet/test/E2E/PreMcpToolCallHookE2ETests.cs	Adds .NET E2E tests for meta set/replace/remove via hook.
dotnet/test/E2E/HookLifecycleAndOutputE2ETests.cs	Updates hook lifecycle assertions to use WorkingDirectory.
dotnet/src/Types.cs	Adds PreMcpToolCallHookInput/Output; renames hook input Cwd properties to WorkingDirectory (wire "cwd").
dotnet/src/Session.cs	Adds hook dispatch for preMcpToolCall and pre-serialization helper for output.
dotnet/src/Client.cs	Updates hasHooks detection to include OnPreMcpToolCall.

Copilot's findings

• Files reviewed: 32/32 changed files
• Comments generated: 4

[github-actions]

Commit pushed: bd6ef76

Generated by Java Codegen Agentic Fix · ● 9.2M

[github-actions]

Generated by SDK Consistency Review Agent for issue #1366 · ● 13.3M

[github-actions]

Cross-SDK Consistency Review

This PR does an excellent job adding preMcpToolCall hook support across Node.js, Python, Go, .NET, and Rust. However, the Java SDK is missing this new hook.

The repository has six language SDKs, and Java is not covered by this PR:

SDK	PreMcpToolCallHook added
Node.js	✅ (nodejs/src/types.ts, nodejs/src/session.ts)
Python	✅ (python/copilot/session.py)
Go	✅ (go/types.go, go/session.go)
.NET	✅ (dotnet/src/Types.cs, dotnet/src/Session.cs)
Rust	✅ (rust/src/hooks.rs)
Java	❌ Missing

What Java needs

To bring Java into alignment, the following would be needed:

1. PreMcpToolCallHookInput — a new class in java/src/main/java/com/github/copilot/sdk/json/ with fields analogous to the other SDKs: serverName, toolName, arguments, workingDirectory, timestamp, and meta (the existing _meta).

2. PreMcpToolCallHookOutput — a new class with a metaToUse field (nullable JsonNode / Map<String, Object>).

3. PreMcpToolCallHandler — a new @FunctionalInterface analogous to PreToolUseHandler.

4. SessionHooks — add onPreMcpToolCall field with getter/setter, and update hasHooks() to include it.

5. CopilotSession.handleHooksInvoke — add a case "preMcpToolCall" branch dispatching to the new handler.

6. E2E tests — follow the pattern in java/src/test/java/.../e2e/ covering the three meta scenarios (set, replace, remove) as done for the other SDKs.

This is a suggestion to maintain feature parity — the PR is otherwise well-structured and consistent across the five SDKs it covers.

Generated by SDK Consistency Review Agent for issue #1366 · ● 5.1M · ◷