## What does this PR do?
Fixes CMake "No jobs found" error during the build-bun step in CI by
using `BUILDKITE_BUILD_NUMBER` instead of `BUILDKITE_BUILD_ID` (UUID)
for the Buildkite API URL.
### Problem
When `BUN_LINK_ONLY=ON`, `SetupBuildkite.cmake` fetches build info from
the Buildkite API to download artifacts from earlier build steps
(build-cpp, build-zig).
The `BUILDKITE_BUILD_ID` environment variable contains a UUID (e.g.,
`019bee3e-da45-4e9f-b4d8-4bdb5aeac0ac`). When this UUID is used in the
URL, Buildkite returns a **302 redirect** to the numeric build number
URL (e.g., `/builds/35708`).
CMake's `file(DOWNLOAD)` command **does not follow HTTP redirects**, so
the downloaded file is empty. Parsing the empty JSON yields 0 jobs,
triggering the fatal error:
```
CMake Error at cmake/tools/SetupBuildkite.cmake:67 (message):
No jobs found:
https://buildkite.com/bun/bun/builds/019bee3e-da45-4e9f-b4d8-4bdb5aeac0ac
```
### Solution
Prefer `BUILDKITE_BUILD_NUMBER` (numeric, e.g., `35708`) when available,
which doesn't redirect. This environment variable is automatically set
by Buildkite.
## How did you verify your code works?
- Verified UUID URL returns 302: `curl -sS -w '%{http_code}'
"https://buildkite.com/bun/bun/builds/019bee3e-da45-4e9f-b4d8-4bdb5aeac0ac"`
→ `302`
- Verified numeric URL returns 200 with JSON: `curl -sS -H "Accept:
application/json" "https://buildkite.com/bun/bun/builds/35708"` → valid
JSON with jobs array
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
## Summary
- Fix CMake JSON parsing error when Buildkite API returns commit
messages with newlines
CMake's `file(READ ...)` reads files with literal newlines, which breaks
`string(JSON ...)` when the JSON contains escape sequences like `\n` in
string values (e.g., commit messages from Buildkite API).
Use `file(STRINGS ...)` to read line-by-line, then join with `\n` to
preserve valid JSON escape sequences while avoiding literal newlines.
## Test plan
- Verify CMake configure succeeds when Buildkite build has commit
messages with newlines
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
