perf(tui): recheck user command folders at most once a second

Found by a read-only Gemini 4 Argon performance review (agy;
CW/artifacts/improve-sweep-20261018/agy-gemini.md, finding 1), confirmed
by reading user_registry.rs.

While a `/` command is in the composer, render() reaches
with_registry_for_workspace through visible_slash_menu_entries on every
frame. That built command_dirs_snapshot_with_plugins before checking
whether anything had changed: two is_workspace_trusted calls (each reads
and parses ~/.codewhale/config.toml and canonicalizes every [projects]
path), plus metadata and read_dir over up to eight command and workflow
directories and every plugin command directory. During streaming that is
dozens of times a second.

The registry state now records when the snapshot was last compared.
Within SNAPSHOT_RECHECK_INTERVAL (1 s) a read for the same workspace and
extension epoch returns the cached registry without touching the disk.
install_plugin_registry still forces a reload (initialized = false), and
an extension-epoch change still reloads at once. Under cfg(test) the
interval is zero, so tests that write a command file and read it back are
unchanged. UserCommandRegistryState drops its unused Clone derive (the new
Mutex field is not Clone).

Live check (debug TUI, cw7087 harness): typed `/zzh` (no match), wrote
~/.codewhale/commands/zzhello.md, then after about 2.5 s the slash menu
listed "/zzhello  test command for the registry recheck"
(slash-after-file.txt in the sweep folder).

Checks: cargo test -p codewhale-tui --lib -- commands:: slash_menu
user_registry user_commands: 1234 passed, 1 failed. The failure is
diagnostics_adapter_projects_full_context_and_prepared_tool_json, which
also failed under the full parallel run earlier today; alone it passed
3/3. cargo check clean; clippy (tui, CI flags) clean.

Not addressed from the same finding: with_registry_for_plugins still
clones the registry and verifies each plugin command's state file on
every call.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NBKbhx19BRbZtvWK8rVKjz

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- While a slash command is in the composer, the TUI rereads your command
+  folders and `config.toml` at most once a second instead of on every frame.
+  A command file you add still shows up in completion within about a second.
 - In a session long enough to fold its oldest transcript cells (past
   5,000), tool details, expanded tool runs, sub-agent cards and a streaming
   reply keep pointing at the right rows. Each fold had shifted them one row

crates/tui/CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- While a slash command is in the composer, the TUI rereads your command
+  folders and `config.toml` at most once a second instead of on every frame.
+  A command file you add still shows up in completion within about a second.
 - In a session long enough to fold its oldest transcript cells (past
   5,000), tool details, expanded tool runs, sub-agent cards and a streaming
   reply keep pointing at the right rows. Each fold had shifted them one row

crates/tui/src/commands/user_registry.rs

@@ -17,7 +17,7 @@ use super::user_commands;
 
 static USER_COMMAND_REGISTRY: OnceLock<RwLock<UserCommandRegistryState>> = OnceLock::new();
 
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Default)]
 struct UserCommandRegistryState {
     initialized: bool,
     workspace: Option<PathBuf>,
@@ -29,6 +29,28 @@ struct UserCommandRegistryState {
     /// reloads when the live extension commands may have changed.
     extension_epoch: u64,
     registry: UserCommandRegistry,
+    snapshot_checked_at: std::sync::Mutex<Option<std::time::Instant>>,
+}
+
+#[cfg(not(test))]
+const SNAPSHOT_RECHECK_INTERVAL: std::time::Duration = std::time::Duration::from_secs(1);
+#[cfg(test)]
+const SNAPSHOT_RECHECK_INTERVAL: std::time::Duration = std::time::Duration::ZERO;
+
+impl UserCommandRegistryState {
+    fn checked_recently(&self) -> bool {
+        self.snapshot_checked_at
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner)
+            .is_some_and(|at| at.elapsed() < SNAPSHOT_RECHECK_INTERVAL)
+    }
+
+    fn mark_checked(&self) {
+        *self
+            .snapshot_checked_at
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner) = Some(std::time::Instant::now());
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -790,6 +812,16 @@ pub fn with_registry_for_workspace<R>(
 ) -> R {
     let workspace = normalize_workspace(workspace);
     let lock = registry_lock();
+    {
+        let guard = lock.read().expect("user command registry lock poisoned");
+        if guard.initialized
+            && guard.workspace == workspace
+            && guard.extension_epoch == crate::extension_host::command::epoch()
+            && guard.checked_recently()
+        {
+            return f(&guard.registry);
+        }
+    }
     let (plugin_sources, plugin_errors) = {
         let guard = lock.read().expect("user command registry lock poisoned");
         if guard.plugin_workspace == workspace {
@@ -806,6 +838,7 @@ pub fn with_registry_for_workspace<R>(
     {
         let guard = lock.read().expect("user command registry lock poisoned");
         if !registry_needs_reload(&guard, &workspace, &snapshot, extension_epoch) {
+            guard.mark_checked();
             return f(&guard.registry);
         }
     }
@@ -827,6 +860,7 @@ pub fn with_registry_for_workspace<R>(
         guard.extension_epoch = extension_epoch;
         guard.registry = replacement;
     }
+    guard.mark_checked();
     f(&guard.registry)
 }