docs(cc608): note that discontinuity recovery is a receiver concern

The stale-caption case after a seek is fixed by the player resetting its 608 decoder state at a discontinuity, as it would any other decoder. The server has no lever here, so livesim2 keeps flipping each segment's first cue rather than skipping it.

Author: tobbee

README.md

@@ -51,8 +51,12 @@ belongs to it, and what it shows for that first cue period depends on its decode
 608 decoder has nothing loaded and shows **no caption**, while one that keeps 608 state
 across the discontinuity flips whatever was last preloaded and can show **one cue of a
 stale caption**. Either way it corrects at the next cue boundary, typically within a
-second. The server cannot avoid this — any pair sent ahead of the `EOC` to clear the
-state would erase the build that is about to be flipped.
+second.
+
+This is a receiver-side matter, not something the server can paper over: any pair sent
+ahead of the `EOC` to clear the state would erase the build that is about to be flipped.
+A player should reset its 608 decoder state on a seek or other discontinuity — which is
+what turns the stale case into the blank one — exactly as it resets any other decoder.
 
 The new `livesim2` software is written in Go instead of Python and designed to handle
 content in a more flexible and versatile way. It is intended to be very easy to install and deploy locally

cmd/livesim2/app/cc608_inject.go

@@ -105,8 +105,10 @@ func cc608PairCount(toks []cta608.Token) int {
 // to it. What it shows for that cue period depends on its decoder state: a fresh
 // decoder has empty non-displayed memory and shows nothing, while one that keeps 608
 // state across the discontinuity flips whatever was last preloaded and can show a
-// stale caption. Either way it is correct from the next cue on, and the server cannot
-// prevent it — an ENM ahead of the EOC would erase the build about to be flipped.
+// stale caption. Either way it is correct from the next cue on. Recovering faster is a
+// receiver-side matter — a player resetting its 608 state on a seek turns the stale
+// case into the blank one — and not something the server can paper over, since an ENM
+// ahead of the EOC would erase the build about to be flipped.
 //
 // Each cue is encoded with a fresh cta608.Encoder so its build is always a complete
 // rebuild. That keeps every EOC paired with a build that fully describes its screen,