Stop a config reload from undoing a change the user just made by hand

Reloading rebuilds the theme and general settings from the config file.
That is right for a file edit, but it also wiped every live `srd set` - and
the titlebar right-click menu's "Customize" rows are built entirely out of
live `srd set`s. Changing a button style from that menu and then saving
init.lua for any unrelated reason silently reverted it.

Survivable while reloads only happened on Mod4+Ctrl+r. The reload-on-write
support added in the previous commit makes a reload happen on every save,
which turns a rare surprise into a reliable one. A control that silently
reverts is worse than no control, so this is a defect rather than a
documented quirk. The AGS peer session reached the same conclusion from the
other side while deciding whether to build Settings controls against these
values, and would have had to label them session-only.

Every setting changed live is recorded on the WindowManager as key -> raw
JSON text, and replayed after each reload through the very same handle_set
that applied it, so a replayed setting cannot behave differently from a real
one. Recorded only on success, so a rejected value is never replayed, and
only for real client calls, so the replay cannot rewrite what it is reading.
Last write wins per key. Raw JSON text because core has no serde dependency
and no reason to gain one for this; the platform crate parses it back.

Verified live in a nested compositor: set button_side left and button_mode
fixed, saved an unrelated config edit, both survived, and the log reported
re-applying two live settings. Three tests cover the round trip, the
rejected-value case and the one-entry-per-key case.

A live value is still a session override rather than a persisted setting.
That distinction is now written down in DEFAULTS.md instead of being a trap.

515 tests pass, clippy clean.

3 files changed, 78 insertions, 0 deletions

diff --git a/crates/platform/src/ipc/dispatch.rs b/crates/platform/src/ipc/dispatch.rs
index d2232c8..749b2aa 100644
--- a/crates/platform/src/ipc/dispatch.rs
+++ b/crates/platform/src/ipc/dispatch.rs
@@ -437,6 +437,44 @@ pub(crate) fn handle_request(line: &[u8], wm: &std::rc::Rc<std::cell::RefCell<Wi
 /// predicate is what the two colour/width arms below walk existing
 /// windows with, rather than touching every window unconditionally.
 fn handle_set(req: &serde_json::Value, wm: &std::rc::Rc<std::cell::RefCell<WindowManager>>) -> (Vec<u8>, bool) {
+    let (response, changed) = apply_set(req, wm);
+    // Recorded only on success, so a rejected value is never replayed --
+    // and only for a real client call, not for the replay itself (see
+    // `replay_live_settings`, which calls `apply_set` directly and would
+    // otherwise rewrite what it is currently reading).
+    if changed {
+        if let (Some(key), Some(value)) = (req.get("key").and_then(|v| v.as_str()), req.get("value")) {
+            wm.borrow_mut().record_live_setting(key, value.to_string());
+        }
+    }
+    (response, changed)
+}
+
+/// Re-applies every setting changed live since startup.
+///
+/// Called after a config reload, which rebuilds the theme and general
+/// settings from the config file and would otherwise silently undo them --
+/// see `WindowManager::live_settings`' own doc comment for why that matters
+/// more now that a reload happens on every save.
+///
+/// Replayed through `apply_set`, the same function that applied them
+/// originally, so a replayed setting cannot behave differently from a real
+/// one. Failures are ignored: a value that no longer applies (a monitor
+/// that has gone away, say) should not stop the rest being restored.
+pub fn replay_live_settings(wm: &std::rc::Rc<std::cell::RefCell<WindowManager>>) -> usize {
+    let recorded = wm.borrow().live_settings();
+    let mut applied = 0;
+    for (key, raw) in recorded {
+        let Ok(value) = serde_json::from_str::<serde_json::Value>(&raw) else { continue };
+        let req = serde_json::json!({ "cmd": "set", "key": key, "value": value });
+        if apply_set(&req, wm).1 {
+            applied += 1;
+        }
+    }
+    applied
+}
+
+fn apply_set(req: &serde_json::Value, wm: &std::rc::Rc<std::cell::RefCell<WindowManager>>) -> (Vec<u8>, bool) {
     let key = req.get("key").and_then(|v| v.as_str()).unwrap_or("");
     let value = req.get("value");
     match key {
diff --git a/crates/platform/src/ipc/mod.rs b/crates/platform/src/ipc/mod.rs
index 796c459..7094f6e 100644
--- a/crates/platform/src/ipc/mod.rs
+++ b/crates/platform/src/ipc/mod.rs
@@ -37,6 +37,7 @@ use std::path::PathBuf;
 use srdwm_core::WindowManager;
 
 mod dispatch;
+pub use dispatch::replay_live_settings;
 mod types;
 #[cfg(test)]
 mod tests;
diff --git a/crates/platform/src/ipc/tests.rs b/crates/platform/src/ipc/tests.rs
index c2a678c..2e61761 100644
--- a/crates/platform/src/ipc/tests.rs
+++ b/crates/platform/src/ipc/tests.rs
@@ -26,6 +26,45 @@ fn read_line(reader: &mut std::io::BufReader<UnixStream>) -> String {
 }
 
 #[test]
+fn a_live_setting_is_recorded_and_survives_a_replay() {
+    // The concrete regression: a config reload rebuilds the theme from the
+    // file, so a value changed by hand (the titlebar menu's own Customize
+    // rows are all live `srd set`s) was silently reverted.
+    let wm = std::rc::Rc::new(std::cell::RefCell::new(WindowManager::new()));
+    let req = serde_json::json!({"cmd": "set", "key": "button_side", "value": "left"});
+    let (_, changed) = super::dispatch::handle_request(serde_json::to_vec(&req).unwrap().as_slice(), &wm);
+    assert!(changed);
+    assert!(wm.borrow().theme.buttons_left);
+
+    // Stand in for what a reload does to the theme.
+    wm.borrow_mut().theme = srdwm_core::ThemeConfig::default();
+    assert!(!wm.borrow().theme.buttons_left, "the rebuild really did drop it");
+
+    assert_eq!(super::replay_live_settings(&wm), 1);
+    assert!(wm.borrow().theme.buttons_left, "the live change must come back");
+}
+
+#[test]
+fn a_rejected_value_is_never_recorded_for_replay() {
+    let wm = std::rc::Rc::new(std::cell::RefCell::new(WindowManager::new()));
+    let req = serde_json::json!({"cmd": "set", "key": "button_side", "value": "sideways"});
+    let (_, changed) = super::dispatch::handle_request(serde_json::to_vec(&req).unwrap().as_slice(), &wm);
+    assert!(!changed, "an invalid value must be rejected");
+    assert_eq!(super::replay_live_settings(&wm), 0, "nothing should have been recorded");
+}
+
+#[test]
+fn setting_the_same_key_twice_replays_only_the_last_value() {
+    let wm = std::rc::Rc::new(std::cell::RefCell::new(WindowManager::new()));
+    for value in ["left", "right"] {
+        let req = serde_json::json!({"cmd": "set", "key": "button_side", "value": value});
+        super::dispatch::handle_request(serde_json::to_vec(&req).unwrap().as_slice(), &wm);
+    }
+    assert_eq!(super::replay_live_settings(&wm), 1, "one entry per key, not one per call");
+    assert!(!wm.borrow().theme.buttons_left, "the last value written is the one that survives");
+}
+
+#[test]
 fn subscribe_gets_an_immediate_snapshot() {
     let dir = tempfile::tempdir().unwrap();
     let mut server = IpcServer::bind_in(dir.path(), "test").unwrap();