Better handling of builders that stop mid-protocol and create premature PRs

[waleedkadous]

Problem

Builders sometimes stop in the middle of a protocol and create PRs before completing all phases. This can happen when:

• The builder hits context limits and loses track of where it is in the protocol
• The builder misinterprets a phase transition and jumps to PR creation
• An error causes the builder to bail out early and try to "save" its work via PR

When this happens, the architect has to manually intervene — the porch state machine doesn't expect a PR at that stage, and there's no clean recovery path.

Desired Outcome

Codev should handle mid-protocol PR creation more gracefully:

• Detect when a builder creates a PR outside the expected protocol phase
• Provide clear recovery options (resume from where it stopped, restart the phase, etc.)
• Better guardrails to prevent premature PR creation in the first place
• Improved state reconciliation when builder state diverges from porch expectations

Notes

This is a recurring pain point. The spec should investigate the failure modes and propose concrete improvements to porch, the builder prompt, or both.