[ci]: fix merge-gate Buildkite state filters

[SolitaryThinker]

Problem

The merge-gate launcher fails before it can schedule Buildkite. Recent runs such as 32933734982 and 32934071377 stop in Cancel previous Buildkite builds with:

jq: Cannot index string with string "env"

The list-builds request sends state=running,scheduled. Buildkite's REST API requires repeated Rails-array parameters for multiple states: state[]=running&state[]=scheduled. The rejected response is an error object, but the current curl -sS still pipes it into a jq filter that assumes an array of builds.

Official contract: https://buildkite.com/docs/apis/rest-api/builds

Solution

• Send one state[] query parameter per requested state.
• Exclude unneeded jobs and expanded pipeline data from this polling request.
• Enable strict shell error handling and make HTTP errors fail the step.
• Validate that the API returned an array of build objects before filtering it.
• Make cancellation request failures visible instead of continuing silently.
• Add a CPU-only workflow contract test so the invalid state encoding and fail-open behavior cannot return.

If the corrected request reports an authorization error, the repository's Buildkite token must be updated to include read_builds; cancellation and build creation require write_builds.

Validation

pytest fastvideo/tests/contract/ -q
  88 passed

pre-commit run --files \
  .github/workflows/ci-trigger-full-suite.yml \
  fastvideo/tests/contract/test_ci_test_collection.py
  passed, including GitHub Actions workflow lint

git diff --check
  passed

[mergify]

Merge Protections

🔴 1 of 1 protections blocking · waiting on 👀 reviews and 🤖 CI

	Protection	Waiting on
🔴	PR merge requirements	👀 reviews and 🤖 CI

🔴 PR merge requirements

Waiting for

• #approved-reviews-by>=1
• check-success=full-suite-passed

This rule is failing.

• #approved-reviews-by>=1
• check-success=full-suite-passed
• check-success=fastcheck-passed
• check-success~=pre-commit
• title~=(?i)^\[(feat|feature|bugfix|fix|refactor|perf|ci|doc|docs|misc|chore|kernel|new.?model|skill|skills|infra)\]

[SolitaryThinker]

/test full

[SolitaryThinker]

/merge

[SolitaryThinker]

Superseded by #1762 at reviewed head 2dc322b60b24507834b447019d71ff75a58adb10. That PR combines the correct repeated Buildkite state filters and strict response validation from this branch with the necessary best-effort cancellation policy, checked cancellation attempts, non-leaking error handling, and CPU contract coverage. Closing this duplicate rather than merging two competing workflow fixes. The unrelated GameCraft T2V SSIM observation from full build #5043 remains tracked by draft diagnostic #1763.