fix(kb-mode): gate prompt sanitization on box-drawing frames (don't touch working prompts)

src/ccbot/handlers/card_model.py

@@ -823,6 +823,13 @@ def render_page(events: list[Event], now: float) -> str:
 # borders mangle the body. We strip them on the kb-mode path.
 _BOX_DRAWING_RE = re.compile(r"[─-▟]")
 _BORDER_ONLY_LINE_RE = re.compile(r"^[\s─-▟]*$")
+# Box-drawing FRAME glyphs (verticals + corners + junctions + double-line),
+# EXCLUDING the plain horizontals ─ ━ which show up as benign dividers in
+# otherwise-normal prompts. Their presence is the signal that Claude Code
+# framed the option previews in boxes (the case that mangles the card). A
+# normal prompt — even one carrying a ── divider — matches none of these, so
+# the sanitize/code-fence path stays a strict no-op for the well-behaved case.
+_BOX_FRAME_RE = re.compile(r"[│┃┌-╋═-╬]")
 
 
 def _sanitize_prompt_block(text: str) -> str:
@@ -872,12 +879,20 @@ def _render_card(
     # keyboard. The regular event log is BELOW the keyboard (footer'd by
     # the keyboard rather than by switcher/pagination). See Task #41.
     if state.in_kb_mode and state.kb_prompt:
-        body = _sanitize_prompt_block(state.kb_prompt)
-        # Render the prompt as a fenced code block so telegramify treats it
-        # as literal monospace: no MarkdownV2 escaping noise, and no
-        # auto-collapse into an expandable blockquote (the "✂ N lines
-        # hidden" artifact). Guard the rare case of a ``` inside the prompt.
-        prompt_part = body if "```" in body else f"```\n{body}\n```"
+        raw = state.kb_prompt
+        if _BOX_FRAME_RE.search(raw):
+            # Claude Code framed the option previews in box-drawing boxes
+            # (┌ │ ├ …). Captured verbatim those borders mangle the body and
+            # telegramify collapses the long region into an expandable
+            # blockquote (the "✂ N lines hidden" artifact). Strip the borders
+            # and render as a fenced code block — literal monospace, no
+            # MarkdownV2 escaping, no blockquote collapse. Guard a stray ```.
+            body = _sanitize_prompt_block(raw)
+            prompt_part = body if "```" in body else f"```\n{body}\n```"
+        else:
+            # No box frame → the long-standing well-behaved prompt. Render it
+            # exactly as before so this fix never alters a normal prompt.
+            prompt_part = raw
         parts = [header, "─────", "⌨ *Waiting for your input:*", prompt_part]
         return "\n".join(parts)
 

tests/test_kb_prompt_sanitize.py

@@ -91,3 +91,42 @@ def test_content_survives_render(self):
         st.kb_prompt = BOXED_PROMPT
         out = _render_card(_sess(), st, user_id=1)
         assert "/data/adb/service.d/99-ccbot.sh" in out
+
+
+# A normal AskUserQuestion with NO box frame — the long-standing working
+# case (incl. a benign ── divider). The fix must be a strict no-op here.
+NORMAL_PROMPT = (
+    "☐ Which approach?\n"
+    "Pick a migration strategy:\n"
+    "❯ 1. Incremental\n"
+    "  2. Big-bang\n"
+    "─────\n"
+    "  3. Chat about this\n"
+    "Enter to select · ↑/↓ to navigate · Esc to cancel\n"
+)
+
+
+class TestNormalPromptUnchanged:
+    """The box-frame gate: a prompt without frame glyphs renders exactly as
+    before — no sanitization, no code fence. Guards the working case."""
+
+    def test_no_frame_means_no_code_fence(self):
+        st = CardState()
+        st.in_kb_mode = True
+        st.kb_prompt = NORMAL_PROMPT
+        out = _render_card(_sess(), st, user_id=1)
+        # The card chrome (header + the literal "─────" separator) is added
+        # by _render_card; the prompt body itself must NOT be code-fenced.
+        body = out.split("⌨ *Waiting for your input:*\n", 1)[1]
+        assert "```" not in body
+        # ...and the prompt is carried verbatim (incl. its own divider).
+        assert NORMAL_PROMPT in out
+
+    def test_divider_only_does_not_trip_the_gate(self):
+        # A ── divider (U+2500) alone is not a frame → no sanitization.
+        assert "❯ 1. Incremental" in NORMAL_PROMPT  # premise
+        st = CardState()
+        st.in_kb_mode = True
+        st.kb_prompt = NORMAL_PROMPT
+        out = _render_card(_sess(), st, user_id=1)
+        assert "❯ 1. Incremental" in out  # cursor/options untouched