Use one current client and daemon protocol

[lydakis]

A missing push checkpoint or snapshot-negotiation endpoint previously triggered an upload using an alternate protocol. Push also accepted both full-manifest and checkpoint-delta requests. The client and daemon now use one current protocol: checkpoint deltas at /push, one workspace-creation endpoint, and required snapshot-negotiation responses. A disabled cache returns 200 OK with all requested hashes missing; absent endpoints fail before upload.

Remove the old-runner placement capability flag and reject descriptors that ignore manifest=omit. Keep frozen-body cache-miss retries, checkpoint-change retries, and uncertain-apply recovery. Small deltas still skip cache negotiation, and complete-upload plans avoid an additional hash map.

CLI presentation changes remain in #12. This branch targets main directly and can be reviewed independently.

Validation:

• Targeted client, daemon, push/watch, workspace creation, cache, descriptor, and placement tests pass with the race detector.
• go vet ./... and the CLI build pass.
• The full race suite reports 19 known environment-related failures (Git status 128 and filesystem mode behavior), with no new failures or race reports.

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, add credits to your account and enable them for code reviews in your settings.