Stage 6 images partial and upload facade

[Leechael]

Summary

• add image-domain query RPCs for templates, discover surface, and media prompt expansion
• add library methods and a top-level expand-prompt command
• route resumable upload through a transport facade and fix image-to-image extraction
• sync upstream planning docs for Stage 6 status

Verification

• go vet ./...
• go test ./... -count=1
• make build
• make ci
• prek
• protocol purity and bypass facade grep checks

---

Summary by cubic

Implements Stage 6 image partials (templates, Discover surface, media prompt expansion) and adds the expand-prompt CLI. Introduces a resumable upload transport facade with correct headers, cookie forwarding, and hardened image-to-image extraction.

• New Features

  • Image RPCs and methods: ListImageTemplates, GetDiscoverSurface, ExpandMediaPrompt, with protocol encoders/decoders and tests.
  • CLI: expand-prompt <text> with optional --json.
  • Upload transport: new facade routes resumable uploads and forwards cookies from the jar.

• Bug Fixes

  • Image-to-image extraction: capture URLs from arr[0]["8"] and ignore marker strings; adds tests.
  • Upload headers: forward Push-Id on both start and finalize; tests now capture handler failures from the server goroutine.

^{Written for commit e0d65ba. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

1 issue found across 23 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="internal/client/transport/upload_test.go">

<violation number="1" location="internal/client/transport/upload_test.go:22">
P2: `t.Fatalf` is called inside the `httptest` handler goroutine. `Fatalf`/`FailNow` must run in the test goroutine, so this can make failures unreliable or flaky. Use non-terminating reporting in the handler (for example `t.Errorf`) and fail from the main test goroutine.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>