feat: add watch print mode

test: refactor test_watch
style: add inline comments for watch

src/lrx_cli/watch/view/print.py

@@ -0,0 +1,44 @@
+"""
+Author: Uyanide pywang0608@foxmail.com
+Date: 2026-04-10 08:15:31
+Description: Print output implementation for watch mode — one shot per track.
+"""
+
+import sys
+
+from . import BaseOutput, WatchState, WatchStatus
+
+
+class PrintOutput(BaseOutput):
+    """Emit full lyrics to stdout once per track transition, then stay silent.
+
+    Deduplication is delegated to the coordinator via position_sensitive=False:
+    the coordinator uses a fixed position for signatures, so on_state fires at
+    most once per (status, track_key) transition rather than on every tick.
+    """
+
+    # fixed position=0 in signatures → coordinator calls on_state only on
+    # track/status transitions, never on lyric cursor advances
+    position_sensitive = False
+
+    plain: bool
+
+    def __init__(self, plain: bool = False) -> None:
+        self.plain = plain
+
+    async def on_state(self, state: WatchState) -> None:
+        if state.status == WatchStatus.FETCHING or state.status == WatchStatus.IDLE:
+            return
+
+        if state.status == WatchStatus.NO_LYRICS:
+            # emit a blank line as a machine-readable sentinel for "track changed, no lyrics"
+            sys.stdout.write("\n")
+            sys.stdout.flush()
+        elif state.status == WatchStatus.OK and state.lyrics is not None:
+            lrc = state.lyrics.normalized
+            if self.plain:
+                text = lrc.to_plain()
+            else:
+                text = str(lrc)
+            sys.stdout.write(text + "\n")
+            sys.stdout.flush()