fix(plugin): keep loading OSD off on warm playlist advance (#317)

* fix(plugin): keep loading OSD off on warm playlist advance

- Track overlay_content_ready_seen when the app sends subminer-overlay-loading-ready
- Skip restarting the "Overlay loading" spinner for an overlay that already reported ready, so it no longer times out into "Overlay did not become ready" (#315)
- Reset the flag on stop, restart, start failure and shutdown
- Add start-gate tests for warm and not-yet-ready playlist advances

* fix(plugin): only report overlay ready once content has loaded

Hide paths dismissed the loading OSD with subminer-overlay-loading-ready,
which the plugin now remembers to skip the spinner on later playlist files.
A hide before the overlay had content would wrongly mark it ready. The app
now sends ready only when the overlay window content is ready, and a new
stop-only subminer-overlay-loading-dismissed message otherwise.

* fix(plugin): resync overlay readiness on dismissal and mpv connect

A dismissal now clears the plugin's readiness flag, since the app sends it
only while its overlay window has no content (e.g. a replaced window).
On mpv (re)connect the app resends subminer-overlay-loading-ready when the
overlay already has content, so a ready signal lost while mpv was away, or
sent before this mpv's plugin existed, still reaches the plugin.

* refactor(main): pass overlay readiness handler directly

plugin/subminer/process.lua

@@ -282,6 +282,19 @@ function M.create(ctx)
 		clear_overlay_loading_osd_deadline()
 	end
 
+	-- Handles the app's subminer-overlay-loading-ready message.
+	local function mark_overlay_content_ready()
+		state.overlay_content_ready_seen = true
+		stop_overlay_loading_osd()
+	end
+
+	-- Handles subminer-overlay-loading-dismissed: the app's current overlay window has no content
+	-- (hidden mid-load, or a replaced window), so earlier readiness no longer applies.
+	local function mark_overlay_content_not_ready()
+		state.overlay_content_ready_seen = false
+		stop_overlay_loading_osd()
+	end
+
 	local function start_overlay_loading_osd()
 		if state.overlay_loading_osd_active then
 			return
@@ -741,6 +754,7 @@ function M.create(ctx)
 
 					state.overlay_running = false
 					state.auto_play_ready_signal_seen = false
+					state.overlay_content_ready_seen = false
 					subminer_log("error", "process", "Overlay start failed after retries: " .. reason)
 					stop_overlay_loading_osd()
 					show_osd("Overlay start failed")
@@ -795,6 +809,7 @@ function M.create(ctx)
 		state.overlay_running = false
 		state.texthooker_running = false
 		state.auto_play_ready_signal_seen = false
+		state.overlay_content_ready_seen = false
 		stop_overlay_loading_osd()
 		disarm_auto_play_ready_gate()
 		show_osd("Stopped")
@@ -934,6 +949,7 @@ function M.create(ctx)
 			state.overlay_running = false
 			state.texthooker_running = false
 			state.auto_play_ready_signal_seen = false
+			state.overlay_content_ready_seen = false
 			state.suppress_ready_overlay_restore = false
 			state.force_ready_overlay_restore = true
 			disarm_auto_play_ready_gate({ resume_playback = false })
@@ -957,6 +973,7 @@ function M.create(ctx)
 					if not success or (result and result.status ~= 0) then
 						state.overlay_running = false
 						state.auto_play_ready_signal_seen = false
+						state.overlay_content_ready_seen = false
 						subminer_log(
 							"error",
 							"process",
@@ -1035,6 +1052,8 @@ function M.create(ctx)
 		disarm_auto_play_ready_gate = disarm_auto_play_ready_gate,
 		start_overlay_loading_osd = start_overlay_loading_osd,
 		stop_overlay_loading_osd = stop_overlay_loading_osd,
+		mark_overlay_content_ready = mark_overlay_content_ready,
+		mark_overlay_content_not_ready = mark_overlay_content_not_ready,
 	}
 end