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Summary

Return non-nil empty completion results for prompt completions and direct non-resource calls to the repository completion handler. Both paths serialize completion values as [], not null.

Why

A successful completion handler returning a typed nil *mcp.CompleteResult can panic during SDK result finalization after request recovery middleware has returned. This fixes the upstream source of that production crash; the remote defense-in-depth wrapper is tracked in github/github-mcp-server-remote#1108.

No upstream issue is associated with this fix. The remote dependency bump is release-dependent and is not included here; no SDK changes are included.

What changed

• Return an empty CompleteResult with an initialized values slice for ref/prompt in CompletionsHandler.
• Return the same non-nil empty result for non-resource calls to RepositoryResourceCompletionHandler.
• Assert non-nil results and JSON values: [] for both paths, and cover unchanged repo:// routing, client errors, unsupported references, and unsupported resource URIs.

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

No tool definitions or schemas change. Empty completion responses now return a valid result instead of a nil pointer; repository resource resolution and error handling are unchanged.

Prompts tested (tool changes only)

• N/A: no tool changes; completion behavior is covered by unit tests.

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

This prevents a completion-result nil-pointer crash without changing authentication, permissions, data exposure, or limits.

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

No tool names change.

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Validation results:

• go test ./pkg/github -run 'Test(CompletionsHandler|RepositoryResourceCompletionHandler)' -count=1 — passed.
• script/lint — passed, 0 issues. The initial automatic linter download stalled; reran successfully using the already-installed matching golangci-lint v2.14.0 binary in the ignored bin/ directory.
• script/test — passed (go test -race ./...).
• go build ./cmd/github-mcp-server — passed.
• git diff --check — passed.

Docs

• Not needed
• Updated (README / docs / examples)

Internal completion bug fix only; no tool definitions, schemas, toolsets, or generated documentation change.

[Copilot]

🟢 Approval recommended

No active review issues are identified, and the change addresses nil completion results with corresponding coverage for result handling and routing.

No open issues 🎉

What changed in this PR

This PR prevents nil completion results from causing SDK finalization panics by returning non-nil empty results that serialize as values: [] for prompt completions and direct non-resource repository completion calls.

Changes:

• Return initialized empty CompleteResult values for both completion paths.
• Preserve existing repository-resource routing and error behavior.
• Add coverage for empty results, JSON serialization, routing, client errors, and unsupported references or URIs.

File	Description
pkg/​github/​server.go	Returns a non-nil empty result for prompt completions.
pkg/​github/​server_test.go	Tests completion routing, errors, non-nil results, and JSON serialization.
pkg/​github/​repository_resource_completions.go	Returns a non-nil empty result for direct non-resource calls.
pkg/​github/​repository_resource_completions_test.go	Expands coverage for empty results and serialization.

_{Review effort: Lite (auto)}