Copilot engine: tool images never reach the model behind the API proxy #76385

Images from tools are dropped for every Copilot workflow that uses a COPILOT_GITHUB_TOKEN, so screenshot- and image-based workflows can't see anything.

Steps

1. Commit any PNG as test.png.
2. Add a workflow_dispatch workflow with engine: copilot and the prompt "Open test.png with the view tool and describe it."
3. Set COPILOT_GITHUB_TOKEN, compile, and run.

Expected: the model receives the image and describes it.

Actual: the model says it can't see the image. On CLI 1.0.106 the view result is only Viewed image file successfully. (an image attachment was omitted from this request because image input is unavailable for the current model). On the default 1.0.103 the omission note is missing too. With COPILOT_PROVIDER_VISION: "true" in engine.env (CLI 1.0.106), the same run describes the image correctly.

Build: gh aw v1.0.1, Copilot CLI 1.0.103 (default) and 1.0.106, ubuntu-latest.

Cause: in API-proxy mode, AWF runs the CLI as an offline BYOK client pointed at the sidecar (copilot-credential-env.ts). The CLI treats BYOK models as text-only unless COPILOT_PROVIDER_VISION=true, which https://github.com/github/copilot-agent-runtime/pull/32179 added (CLI 1.0.106 and later; documented in copilot help environment).

Suggested fix: set COPILOT_PROVIDER_VISION=true alongside COPILOT_OFFLINE in GitHub-token mode, and move DefaultCopilotVersion to 1.0.106 or later.

Workaround:

engine:
  id: copilot
  version: "1.0.106"
  checksums-sha256: "5e8cf7427cc69cc757d1a08132dac0eb9e7f56c95d269ecbc06799686e996730" # SHA256SUMS.txt
  env:
    COPILOT_PROVIDER_VISION: "true"

Related: #74972, github/copilot-cli#4600

🤖 Authored with GitHub Copilot on behalf of @rwoll.