Add server-side branch prefix search and cursor pagination for GitHub

[HarshMN2345]

Uses GraphQL refs query with query variable for prefix filtering and cursor-based pagination instead of fetching all branches client-side.

[greptile-apps]

Greptile Summary

This PR migrates listBranches from a REST call to a GitHub GraphQL refs query, adding server-side search filtering and cursor-based pagination via a new $search parameter and a struct return type. It also fixes getLatestCommit to gracefully handle null author fields that occur on commits made by GitHub App installations.

• listBranches now returns array{items, hasNext, nextCursor} instead of a flat array<string>; the null-repository case (data.repository: null) is correctly guarded with is_array() before any array access, and pagination state is read from GraphQL's own pageInfo rather than a client-side probe.
• getLatestCommit no longer throws when author is null; instead commitAuthorAvatar and commitAuthorUrl fall back to empty strings, which is appropriate for App-installation commits.
• Tests are updated throughout to assert the new struct shape and exercise three-page cursor navigation and search-filtered pagination.

Confidence Score: 4/5

Safe to merge with awareness that the adapter contract change is intentionally staged; no runtime bugs found in the current implementation.

The GraphQL implementation is logically correct — null-repository is guarded before any array access, pageInfo.hasNextPage is used directly so no extra round-trip or probe arithmetic is needed, and the getLatestCommit author-null fix is sound. Unresolved concerns from prior review discussion (documentation inconsistency between 'prefix' in the PHPDoc and 'substring' in the test comment, and the silent fallback when an integer $page > 1 is passed) are present in the merged code but do not cause runtime failures in typical usage.

src/VCS/Adapter/Git/GitHub.php — specifically the $search parameter documentation and the integer $page silent-fallback behaviour.

Important Files Changed

Filename	Overview
src/VCS/Adapter/Git/GitHub.php	Replaces REST-based listBranches with GraphQL cursor pagination and adds $search param; also fixes getLatestCommit to tolerate null author from App installations. Null-repository case is handled correctly via is_array() guard. Documentation inconsistency (PHPDoc says "Prefix filter" but code/test describes substring behaviour) and silent fallback for integer $page > 1 remain from prior review threads.
tests/VCS/Adapter/GitHubTest.php	Tests updated to assert the new struct return shape; cursor-based pagination flow is fully exercised across three pages. Existing clone/owner/search tests moved earlier in the file. No functional test regressions observed.

_{Reviews (5): Last reviewed commit: "Remove client-side prefix filter — trust..." | Re-trigger Greptile}

[greptile-apps]

Silent fallback for integer $page values other than 1 may surprise callers

A caller passing $page = 3 silently gets the first page with no error or warning. Consider throwing an \InvalidArgumentException for integer values > 1, or explicitly marking those values as unsupported.

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