v0.8.63: Add first-class sub-agent toggle

[BovmantH]

Summary

• Add /config subagents on|off|status plus /config features.subagents true|false as first-class controls for the existing features.subagents flag.
• Keep session-only changes live by wiring AppAction::UpdateFeatures through Op::SetFeatures; persisted changes write [features] subagents = ....
• Make only features.subagents editable in the native /config Experimental section, and document the difference between the global feature flag and [subagents] max_depth = 0.
• Applied Gemini code review suggestions: persist before updating in-memory state, use eq_ignore_ascii_case for efficiency.

Closes #3305.

Verification

• cargo fmt -- --check
• cargo test -p codewhale-tui --bins subagent
• cargo test -p codewhale-tui --bins set_features_op_emits_runtime_update_status
• cargo test -p codewhale-tui --bins config_view_includes_expected_editable_rows
• cargo test -p codewhale-tui --bins config_view_experimental_features_show_effective_state_and_overrides

[greptile-apps]

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[github-actions]

Thanks @BovmantH for taking the time to contribute.

This repository is observing a maintainer-managed PR intake gate in dry-run mode, so this pull request is staying open. This note helps maintainers prepare the allowlist before any enforcement is considered.

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

[gemini-code-assist]

Code Review

This pull request introduces first-class TUI controls and dynamic configuration support for the subagents feature flag. It allows users to check, toggle, and persist the subagents feature flag via /config subagents commands, updates the experimental configuration view to make this flag editable, and refactors the engine to support updating feature flags dynamically at runtime. Documentation has also been updated to clarify the distinction between the global subagents feature flag and the max_depth limit. Feedback suggests making the key matching in is_subagents_config_key more robust by converting the key to lowercase and supporting hyphenated variants under the features. and feature. prefixes.

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[gemini-code-assist]

To make the key matching more robust and user-friendly, we should:

1. Convert the input key to lowercase (using to_ascii_lowercase()) to ensure case-insensitive matching when queried via /config (since show_single_setting might not lowercase the key).
2. Support hyphenated variants under the features. and feature. prefixes (e.g., features.sub-agents and feature.sub-agents) for completeness, since sub-agents is already supported as a standalone key.

Suggested change

	fn is_subagents_config_key(key: &str) -> bool {
	matches!(
	key,
	"subagents" | "sub-agents" | "features.subagents" | "feature.subagents"
	)
	}
	fn is_subagents_config_key(key: &str) -> bool {
	matches!(
	key.to_ascii_lowercase().as_str(),
	"subagents"
	| "sub-agents"
	| "features.subagents"
	| "features.sub-agents"
	| "feature.subagents"
	| "feature.sub-agents"
	)
	}

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