fix(tui): persist provider switches to config

[xyuai]

Summary

• persist /provider switches back to config.toml so restart behavior matches the active provider
• keep the saved settings provider in sync and surface a warning if persistence fails
• add a regression test covering the Arcee -> Xiaomi MiMo split-state path from provider switching: settings/config split can mix MiMo model with Arcee base URL #2663

Fixes #2663.

Greptile Summary

This PR fixes a stale-restart bug (#2663) where switching providers via /provider in the TUI was not written back to config.toml, so the next launch would revert to the previously configured provider. The fix wraps both persist_root_string_key (config.toml write) and Settings::load/save in a single closure; on any error the switch still takes effect in memory but a visible warning is appended to the chat and status bar.

• ui.rs: switch_provider now always calls commands::persist_root_string_key to update config.toml and separately updates Settings, surfacing a non-fatal warning instead of silently ignoring persistence failures.
• tests.rs: New regression test provider_switch_persists_provider_to_config_for_restart covers the Arcee → XiaomiMimo split-state path from provider switching: settings/config split can mix MiMo model with Arcee base URL #2663, asserting both the in-memory config and the file reloaded from disk agree on the new provider.

Confidence Score: 4/5

Safe to merge — the persistence logic is correct and failures are surfaced as a user-visible warning rather than crashing or silently dropping the switch.

The core fix is straightforward and well-tested: the new regression test verifies the on-disk config, in-memory state, and settings all agree after a switch. The only findings are cosmetic — non-idiomatic newline literals and an arrow character that diverges from the style used by adjacent messages.

No files require special attention; the two style issues are both confined to the new lines in ui.rs.

Important Files Changed

Filename	Overview
crates/tui/src/tui/ui.rs	Adds config.toml persistence to switch_provider via persist_root_string_key; logic is correct but uses non-idiomatic char::from(10) for newlines and ASCII -> instead of the Unicode → used by adjacent messages.
crates/tui/src/tui/ui/tests.rs	New regression test covers the Arcee → XiaomiMimo split-state path, asserting in-memory config, on-disk config, and settings all agree on the switched provider; test structure and assertions look correct.

Sequence Diagram

sequenceDiagram
    participant User
    participant TUI as TUI (switch_provider)
    participant Engine
    participant ConfigTOML as config.toml
    participant Settings as settings.json

    User->>TUI: /provider xiaomi-mimo
    TUI->>TUI: "Update in-memory Config & App state"
    TUI->>Engine: Op::Shutdown
    TUI->>Engine: spawn_engine (new provider)
    TUI->>Engine: Op::SyncSession / Op::SetCompaction

    note over TUI,Settings: Persistence closure (errors become a warning, never block the switch)
    TUI->>ConfigTOML: persist_root_string_key("provider", "xiaomi-mimo")
    alt write succeeds
        ConfigTOML-->>TUI: Ok(path)
        TUI->>Settings: Settings::load()
        Settings-->>TUI: settings
        TUI->>TUI: "settings.default_provider = "xiaomi-mimo""
        TUI->>Settings: settings.save()
        TUI->>User: "Provider switched: Arcee → XiaomiMimo" (no warning)
    else any step fails
        TUI->>User: "Provider switched … (not fully persisted)"
    end

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_{Reviews (1): Last reviewed commit: "fix(tui): persist provider switches to c..." | Re-trigger Greptile}

Greptile also left 2 inline comments on this PR.

[github-actions]

Thanks @xyuai for taking the time to contribute.

This repository is currently observing a maintainer-managed contribution gate in dry-run mode, so this pull request is staying open. When enforcement is enabled, pull requests from contributors who are not listed in .github/APPROVED_CONTRIBUTORS will be closed automatically.

Please read CONTRIBUTING.md for the expected contribution shape. A maintainer can grant PR access by commenting /lgtm on a pull request.

[gemini-code-assist]

Code Review

This pull request updates the provider switching logic in the TUI to persist the selected provider to the configuration file, handling potential errors and displaying a warning if persistence fails. It also adds a corresponding integration test to verify this behavior. The review feedback suggests simplifying the construction of the switch_summary string by using a single format! macro call and using the idiomatic '\n' character instead of char::from(10).

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[gemini-code-assist]

The string construction for switch_summary can be simplified and made more idiomatic. Instead of manually pushing newlines via char::from(10) and allocating a temporary string with format! for the model transition, you can combine the initial message and the model transition into a single format! call. Additionally, using '\n' is the standard, idiomatic way to append a newline character in Rust.

    let mut switch_summary = format!(
        "Provider switched: {} -> {}\nModel: {} -> {}",
        previous_provider.as_str(),
        target.as_str(),
        previous_model,
        new_model
    );
    if let Some(ref warning) = persist_warning {
        switch_summary.push('\n');
        switch_summary.push_str(warning);
    }

[greptile-apps]

char::from(10) is a non-idiomatic way to express a newline in Rust and makes the intent harder to read at a glance. The idiomatic form is the ' ' literal, which the rest of the codebase already uses in format strings.

Suggested change

	switch_summary.push(char::from(10));
	switch_summary.push_str(&format!("Model: {} -> {}", previous_model, new_model));
	if let Some(ref warning) = persist_warning {
	switch_summary.push(char::from(10));
	switch_summary.push('\n');
	switch_summary.push_str(&format!("Model: {} -> {}", previous_model, new_model));
	if let Some(ref warning) = persist_warning {
	switch_summary.push('\n');

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[greptile-apps]

The adjacent model/thinking change messages (lines 5215–5257) consistently use the Unicode right arrow →, but the new provider-switch message uses the ASCII two-character sequence ->. The inconsistency is visible to users who see both types of messages in the same session.

Suggested change

	let mut switch_summary = format!(
	"Provider switched: {} -> {}",
	previous_provider.as_str(),
	target.as_str(),
	);
	switch_summary.push(char::from(10));
	switch_summary.push_str(&format!("Model: {} -> {}", previous_model, new_model));
	let mut switch_summary = format!(
	"Provider switched: {} → {}",
	previous_provider.as_str(),
	target.as_str(),
	);
	switch_summary.push('\n');
	switch_summary.push_str(&format!("Model: {} → {}", previous_model, new_model));

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[Hmbown]

Cherry-picked to codex/v0.8.53 in dba332e with endpoint display merged.