## Why
Changing the default model provider should not prevent users from resuming or continuing a thread that uses another configured provider.
## What changed
- Resolve cold resumes using the thread's saved provider and reject explicit attempts to switch it on resume.
- Use retained provider configuration for loaded threads without reloading the current default selection, while continuing to enforce managed provider policy.
- Preserve errors for missing provider definitions and policy conflicts.
## Testing
Update app-server and TUI coverage for resuming with a different default, recovering after restoring a missing provider definition, preserving drafts across resume retries, and continuing loaded threads with malformed system defaults.
GitOrigin-RevId: c5bf3b03cacde7349480c94c2f10bac827a0eb1f
## Why
Switching model providers can hide saved chats from resume lookup or prevent them from opening. Keep their history readable when the server rejects resuming because of a provider mismatch, missing configuration, or policy conflict.
## What changed
- Include all providers in the resume picker, named resume lookup, and `resume --last`, while retaining provider filtering for fork lookup.
- Open chats with provider errors as read-only history and show an explanation with recovery shortcuts: `c` to continue in a new chat, `n` to start fresh, and `Esc` to choose another chat.
- Continuing in a new chat prepares an editable, unsent prompt referencing the saved conversation.
- Preserve drafts and rejected prompts or steers, suppress automatic submission, and retry provider admission when reopening the chat.
## Testing
Add coverage for cross-provider discovery, read-only history, configuration recovery, continuation drafts, rejected input recovery, error rendering, and Escape handling during transcript browsing.
GitOrigin-RevId: 5aaa7a404b9a6231101599adef18d2f1e4a8020a
## Why
Existing chats retain their provider configuration when the selected provider changes. Reject resume and input until the configured provider matches the chat, while keeping history readable and allowing recovery after configuration is restored.
## What changed
- Validate saved providers before applying resume overrides, preserving the provider when only model or reasoning settings change.
- Check the current provider selection, including profiles and launch overrides, before accepting input. Reject input when configuration cannot be loaded.
- Return structured `ModelProviderError` data for provider mismatches, missing definitions, and policy conflicts, with generated JSON Schema, TypeScript, and Python types.
## Testing
Add coverage for override bypass prevention, provider restoration, readable history after rejection, and blocked requests sending no inference traffic. Verify schema fields and Python round trips match the error wire format.
GitOrigin-RevId: 051f97c3815c547d8411c71b770df30eae969f68
## Why
Client provider defaults can override the app server's configured provider and hide its sessions from resume and fork history.
## What changed
- Omit implicit provider overrides from thread start, resume, and fork requests so the server can resolve its defaults.
- Use the server's effective provider for named history lookup, `--last`, and resume and fork pickers, while honoring explicit CLI and selected-profile choices.
- Respect managed provider requirements when resolving history filters and preserve the active session's provider when forking it.
## Testing
Add app-server regression tests for provider defaults, explicit choices, configuration changes, selected profiles, and managed requirements. Add CLI coverage for resume and fork pickers and `--last` with local daemon and embedded servers, plus a picker rendering snapshot.
GitOrigin-RevId: a077758b13a5e55552b52e5532ad4bebe86dce7e
Abhinav