Piped v1 Cloud Run plugin panics on deployment and livestate entry points

What happened:

The piped v1 Cloud Run plugin exposes deployment and livestate entry points that still call panic("implement me"). Any request that reaches ExecuteStage, DetermineVersions, DetermineStrategy, or GetLivestate will crash the plugin process instead of returning a controlled error.

What you expected to happen:

Cloud Run plugin requests should either complete successfully or return an explicit error without panicking the process.

How to reproduce it:

1. Open pkg/app/pipedv1/plugin/cloudrun/deployment/plugin.go and pkg/app/pipedv1/plugin/cloudrun/livestate/plugin.go.
2. Inspect Plugin.ExecuteStage, Plugin.DetermineVersions, Plugin.DetermineStrategy, and Plugin.GetLivestate.
3. Invoke any of those exported methods from a focused unit test or a small harness.
4. Observe that the current implementation panics immediately because each method ends in panic("implement me").

Environment:

• piped version: repository checkout on 2026-07-07
• control-plane version: repository checkout on 2026-07-07
• Others: reproduced from current master checkout by static inspection of the exported Cloud Run plugin handlers

Summary

The v1 Cloud Run plugin binary is registered with both deployment and livestate handlers, but several required methods are still stubbed with panics.

Affected Area

pkg/app/pipedv1/plugin/cloudrun

Steps to Reproduce

1. Build or inspect the Cloud Run v1 plugin module.
2. Call ExecuteStage, DetermineVersions, or DetermineStrategy on deployment.Plugin.
3. Call GetLivestate on livestate.Plugin.
4. Observe process termination from panic("implement me") instead of an error response.

Expected Behaviour

Cloud Run plugin handlers should never crash the plugin process. Unsupported behavior should be reported through explicit errors until full implementations exist.

Actual Behaviour

The exported handlers panic immediately, which can terminate the plugin process when those code paths are exercised.

Technical Evidence

• pkg/app/pipedv1/plugin/cloudrun/deployment/plugin.go:51-63
• pkg/app/pipedv1/plugin/cloudrun/livestate/plugin.go:27-29
• pkg/app/pipedv1/plugin/cloudrun/main.go registers both deployment and livestate plugins through sdk.NewPlugin(...), so these panic paths are part of the published plugin surface.

Suspected Root Cause

The Cloud Run v1 plugin skeleton was merged before deployment and livestate handler implementations were completed.

Proposed Direction

Replace the panic stubs with explicit returned errors for unsupported operations, or gate registration of unfinished handlers until complete implementations are ready. Add regression tests covering each handler so future changes cannot reintroduce process panics.

Acceptance Criteria

• Cloud Run plugin deployment and livestate entry points no longer panic.
• Unsupported operations return explicit errors instead.
• Focused unit tests cover ExecuteStage, DetermineVersions, DetermineStrategy, and GetLivestate.

Start with pkg/app/pipedv1/plugin/cloudrun/deployment/plugin.go and pkg/app/pipedv1/plugin/cloudrun/livestate/plugin.go, then inspect registration in pkg/app/pipedv1/plugin/cloudrun/main.go. Exercise ExecuteStage, DetermineVersions, DetermineStrategy, and GetLivestate from focused unit tests. Done means these entry points no longer panic, unsupported operations return explicit errors, and regression tests cover each handler.