docs: finish dropping the stripped-newline rule from the input docs

The first commit left the old rule standing in places: the gotchas list in
extending-codeman.md still said newlines were stripped and that
"echo A\necho B\r" ran `echo Aecho B`, and so did both READMEs and the
skill's big-input section. Those now describe the paste.

Newlines are only kept on the mux path, so the docs that describe the paste
say "with useMux": without it a multi-line body is not a plain prompt and is
written straight into the pane.

Cron keeps rejecting multi-line prompts, but its docs and the code comments
in cron-service.ts, schemas.ts and respawn-controller.ts gave a reason this
change removes (writeViaMux joining lines, a newline submitting in Ink). The
reason that remains is the submit check, which cannot recognise a
multi-line paste in the composer, and for cron's paste mode the newlines
reaching the CLI as keys.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/extending-codeman.md

@@ -294,8 +294,8 @@ if ! jq -e '.data.wait.matched' <<<"$R" >/dev/null; then
 fi
 
 # 3. Send the prompt AND register the wait in one call, so the answer cannot be
-#    the previous turn's idle state. Single line only, ending in \r (otherwise
-#    Enter is never sent and this wait times out on a turn that never started).
+#    the previous turn's idle state. It must end in \r (otherwise Enter is never
+#    sent and this wait times out on a turn that never started).
 W=$("${CURL[@]}" -X POST "$API/api/v1/sessions/$SID/input" \
   -H 'Content-Type: application/json' \
   -d '{"input":"Run the test suite and summarize the failures\r","useMux":true,
@@ -414,14 +414,16 @@ Every one of these has cost somebody real time.
   shipped bugs more than once.
 - **`text/plain` bodies stay raw.** Auto-parsing them as JSON enabled
   simple-request CSRF, so it is deliberate. Send `application/json`.
-- **Prompts are single-line and must end with `\r`.** The server splits your text
-  and Enter into two separate tmux writes (Ink needs them apart), but it sends the
-  Enter **only when the input contains a carriage return**. Without it your text
-  sits on the prompt unsubmitted, which is the single most common "the wait
-  endpoints don't work" report: the wait runs its full timeout on a turn that never
-  started. Newlines inside the string are stripped rather than rejected, so
-  `"echo A\necho B\r"` runs the single joined command `echo Aecho B`: send one line
-  per call.
+- **Prompts must end with `\r`.** The server splits your text and Enter into two
+  separate tmux writes (Ink needs them apart), but it sends the Enter **only when
+  the input contains a carriage return**. Without it your text sits on the prompt
+  unsubmitted, which is the single most common "the wait endpoints don't work"
+  report: the wait runs its full timeout on a turn that never started. With
+  `useMux`, newlines inside the string are kept: the text goes in as one paste and
+  the Enter after it submits all of it, so `"echo A\necho B\r"` runs both commands
+  in a shell. The check that re-presses a stranded Enter cannot reliably recognise
+  a multi-line paste, so a long multi-line prompt to a just-started agent is still
+  safer in a file it is told to read.
 - **`wait-output`'s `from=now` is not "printed after you asked".** tmux repaints
   the visible screen on attach, on resize, and on any TUI redraw, and a repaint
   arrives as ordinary output, so text already on screen can satisfy a fresh wait.