docs(terminal): correct two delivery-accounting comments that misstate the mechanism

`parkedCharsByPty` was documented as cumulative. It is a live balance,
decremented as each chunk settles, and the write-off subtracts it from a
genuinely cumulative `receivedChars` — mixing the two up is how someone
re-derives the predicate wrongly.

The "pauses the shell" claim is only true for ASCII-dominant output. This
buffer caps at 512KB of UTF-8 bytes while main's window counts UTF-16 chars,
so multi-byte output evicts and settles before main's window ever fills.

src/renderer/src/components/terminal-pane/pty-parked-delivery-debt.ts

@@ -6,7 +6,9 @@
  * call a wedge, so it was blind by construction, and the producer was never paused — main
  * kept flooding a pane nobody could see. Holding the credit turns parked bytes into real
  * debt, which is what makes main's existing per-PTY window pause the shell, the watchdog
- * see the pane, and the write-off lane able to forgive it.
+ * see the pane, and the write-off lane able to forgive it. The pause is not guaranteed: this
+ * buffer caps at 512KB of UTF-8 BYTES while main's window counts UTF-16 CHARS, so on
+ * multi-byte output eviction settles the credit before main's window ever fills.
 
  *
  * Unit is delivery-credit CHARS (`rawLength ?? data.length`), never the buffer's UTF-8 byte

src/shared/pty-renderer-delivery-health.ts

@@ -19,8 +19,11 @@ export type PtyRendererDeliveryStateReport = {
    *  ACK path and resync response carry; merging them here is a free extra
    *  repair lane for the lost-ACK variant. */
   processedCharsByPty: Record<string, number>
-  /** Cumulative chars received for a PTY that has no registered data handler and
-   *  are parked in the renderer's pre-handler buffer. Their ACK is withheld, so —
+  /** Chars CURRENTLY parked for a PTY with no registered data handler — a live balance,
+   *  decremented as each chunk settles, not a cumulative total like the fields either side
+   *  of it. `writeOffLostRendererDelivery` subtracts it from a cumulative `receivedChars`
+   *  precisely because of that: what is still parked is what cannot repay itself. Their ACK
+   *  is withheld, so —
    *  unlike received-but-unparsed bytes, which their own deferred ACK repays —
    *  this debt has no consumer to repay it and only a write-off or a bind clears
    *  it. Absent means "none parked", which is exactly how an older renderer read. */