fix(ui_get): bound pagination to cap latency

[mattdholloway]

Problem

ui_get backs a synchronous UI picker — the label/assignee/milestone/branch/reviewer dropdowns in the MCP App issue/PR write surfaces. Each handler paginated GitHub API results in an unbounded loop (PerPage: 100, looping until NextPage == 0 / HasNextPage == false).

On very large repos/orgs this fans out into dozens of sequential API round-trips, and a single slow/stalled page inflates the whole call. Production telemetry showed ui_get p50 at sub-second but the tail spiking to ~20 minutes (max/p99 ~1.17M–1.29M ms).

Fix

Bound every ui_get pagination loop to a shared package-level constant uiGetMaxPages = 10 (≈1000 items at PerPage 100) and add an additive has_more boolean to each response indicating results were deliberately truncated. The tool is now fast-or-bounded instead of unbounded.

Truncation is an accepted product behavior here: the picker pairs it with typeahead, so responsiveness matters more than completeness.

has_more is computed as "there were more pages we deliberately did not fetch":

• REST loops: page cap hit and resp.NextPage != 0.
• GraphQL labels loop: page cap hit and PageInfo.HasNextPage still true.
• uiGetReviewers: true if either the collaborators loop or the teams loop was truncated.

Affected methods

Method	Pagination	Notes
uiGetLabels	GraphQL cursor loop	totalCount stays the server-reported full repo count, so len(labels) < totalCount when truncated — expected
uiGetAssignees	REST	totalCount = len(result) (bounded count)
uiGetMilestones	REST	totalCount = len(result)
uiGetBranches	REST	totalCount = len(result)
uiGetReviewers	two REST loops (collaborators + teams)	shared has_more

uiGetIssueTypes and issue_fields are single-request (no loop) and intentionally left unchanged.

[Copilot]

Pull request overview

This PR bounds pagination in the ui_get tool’s synchronous picker endpoints to cap tail latency on large repos/orgs, and surfaces intentional truncation to the UI via an additive has_more response field.

Changes:

• Introduces a shared uiGetMaxPages cap and applies it to all paginated ui_get handlers (REST and GraphQL).
• Adds has_more to paginated handler responses to indicate deliberate truncation when the page cap is hit.
• Extends pkg/github/ui_tools_test.go with within-cap and truncation test cases (including a custom transport for multi-page GraphQL label queries).

Show a summary per file

File	Description
pkg/github/ui_tools.go	Caps ui_get pagination loops and emits has_more when results are truncated due to the cap.
pkg/github/ui_tools_test.go	Adds/extends tests to validate the page cap behavior and has_more semantics for bounded and truncated cases.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0