Add ifc label for search_repositories tool

[gokhanarkan]

Emits an IFC SecurityLabel on the search_repositories tool result when the InsidersMode flag is enabled, mirroring the pattern landed for get_me (#2432), list_issues (#2453), get_file_contents (#2454), search_issues (#2456), and issue_read (#2457).

Refs github/copilot-mcp-core#1623, github/copilot-mcp-core#1389. The last ingress tool from #1623's table.

Chained on #2457 (which is itself chained on #2456). GitHub will auto-retarget the base to main as the upstream PRs merge.

What this PR does

Search results may span multiple repositories, so _meta.ifc for search_repositories is the IFC meet of the per-repository labels — same semantics as search_issues (#2456) after Joanna's review:

• Integrity is always untrusted (repository names, descriptions, and topics are user-authored).
• Confidentiality follows the IFC meet (greatest lower bound): private wins. A reader of the combined result must be authorised to read every matched private repository.
  • Empty result set → ["public"] (no data leaked).
  • All matched repos public → ["public"].
  • Otherwise → intersection of the collaborator sets across the private matches only (public repos contribute the universe set and drop out of the intersection without shrinking it).

If any per-repo collaborators lookup fails, the label is omitted entirely (consistent with get_file_contents, search_issues, and issue_read) to avoid misclassifying the result.

Helper consolidation

The math is identical to search_issues, so the helper has been renamed and is now shared:

• ifc.LabelSearchIssues → ifc.LabelSearchMultiRepo in pkg/ifc/ifc.go. Both search_issues and search_repositories call the same join function.
• Removed the previous constant LabelSearchRepositories() (which returned PublicUntrusted()).
• New attachSearchRepositoriesIFCLabel in pkg/github/search.go iterates result.Repositories, reads repo.GetPrivate() directly off the search response (no extra visibility API call), and fetches collaborators only for private hits.

Cost per request: 0 calls for an all-public result; N calls for N private matches (collaborators only). Cheaper than search_issues because visibility comes for free on the repository search payload.

Tests

Test_SearchRepositories_IFC_InsidersMode in pkg/github/search_test.go with 6 subtests mirroring the search_issues coverage:

1. Insiders off → result.Meta == nil.
2. Insiders on, all public → integrity=untrusted, confidentiality=["public"].
3. Insiders on, mixed public + private → readers = the private repo's collaborator set (private wins).
4. Insiders on, two private repos → intersection of collaborator sets.
5. Insiders on, collaborators lookup fails (500) → no ifc meta.
6. Insiders on, empty results → ["public"].

Validation

• go test -race ./... — green.
• gofmt -s clean; go vet ./... clean.
• (./script/lint itself fails locally with a pre-existing golangci-lint Go-version mismatch unrelated to this change.)
• No tool schema/annotation changes → no toolsnap or README regeneration needed.

[Copilot]

Pull request overview

Adds IFC (_meta.ifc) annotation to the search_repositories MCP tool output when InsidersMode is enabled, aligning search_repositories with the existing IFC-labeling pattern used across other ingress tools.

Changes:

• Added ifc.LabelSearchRepositories() returning a constant PublicUntrusted() label for repository search results.
• Updated SearchRepositories to attach _meta.ifc on successful responses when deps.GetFlags(ctx).InsidersMode is true.
• Added unit test coverage verifying IFC metadata is omitted when insiders mode is off and present (public/untrusted) when on.

Show a summary per file

File	Description
pkg/ifc/ifc.go	Adds LabelSearchRepositories() helper documenting/encapsulating the label decision for search_repositories.
pkg/github/search.go	Attaches _meta.ifc to search_repositories successful results behind InsidersMode.
pkg/github/search_test.go	Adds Test_SearchRepositories_IFC_InsidersMode covering both insiders on/off behavior.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0

The base branch was changed.