Frame Claude Code's errors into the compact pane

The compact pane is prompt-only because the feed above shows the context.
An error is the exception: the feed cannot show it. A tool_result only
reaches us with the next request, which a turn that died never sends, and
an `API Error` row is Claude Code's own text, never in the stream at all.

So the frame walks further up to take the report in, and the scheduled
ctrl-l wipe is cancelled while one is framed — Ink redraws only the live
frame, so wiping would delete the error 400ms after it appeared.

Detection is text shape, not colour: the tool error renders palette 211
and the API error 220, both theme values. ERROR_SCAN is the only bound,
which is what makes it self-limiting — the error drifts out of the window
as the next turn prints output and the pane shrinks back on its own.

dev/fake_upstream.py

@@ -8,7 +8,7 @@ ExitPlanMode, TodoWrite/Task*) on demand, so the pane's frame detector in
 `src/term.rs` can be developed against what Ink actually draws.
 
 Scenario is picked per turn from `CT_FAKE_SCENARIO`
-(ask | plan | todo | taskupdate | agent | websearch | ansi | text).
+(ask | plan | todo | taskupdate | agent | websearch | ansi | toolerror | apierror | text).
 
 `websearch` also answers the *nested* request Claude Code makes to run WebSearch:
 that call declares Anthropic's server-side `web_search` tool, so it is replied to
@@ -162,6 +162,12 @@ ANSI_INPUT = {
 }
 
 
+# A tool call that *fails* on the child's side, so Claude Code prints its own
+# red error row (`⎿  Error: …`) above the input box. `Read` is auto-approved, so
+# this needs no permission prompt — the failure comes from the missing file.
+TOOL_ERROR_INPUT = {"file_path": "/nonexistent/claude-cloak/does-not-exist.txt"}
+
+
 ASK_INPUT = {"questions": [{
     "question": "The compact pane currently crops the top of this prompt. Which framing "
                 "should the pane use when an interactive question is on screen, given that "
@@ -269,6 +275,21 @@ class Handler(BaseHTTPRequestHandler):
             return
 
         scenario = read_scenario()
+        # `apierror`: a non-retryable upstream failure, so Claude Code prints
+        # its own red `API Error: 400 …` row where the turn would have been.
+        # Only the *turn* request fails — the side/title calls still answer, so
+        # the pane behaves normally around the error.
+        if scenario == "apierror" and tools and not hosted and not has_result:
+            out = json.dumps({"type": "error", "error": {
+                "type": "invalid_request_error",
+                "message": "fake upstream rejected this turn on purpose"}}).encode()
+            self.send_response(400)
+            self.send_header("content-type", "application/json")
+            self.send_header("content-length", str(len(out)))
+            self.end_headers()
+            self.wfile.write(out)
+            return
+
         # The nested hosted-tool request answers itself, whatever the scenario.
         if hosted:
             gen = stream_server_websearch()
@@ -300,6 +321,10 @@ class Handler(BaseHTTPRequestHandler):
                               "Let me search for that.")
         elif scenario == "ansi":
             gen = stream_tool("Bash", ANSI_INPUT, "Printing coloured output.")
+        elif scenario == "basherror":
+            gen = stream_tool("Bash", {"command": "echo boom >&2; exit 3", "description": "Fail"}, "Running that.")
+        elif scenario == "toolerror":
+            gen = stream_tool("Read", TOOL_ERROR_INPUT, "Reading that file.")
         elif scenario == "taskupdate":
             gen = stream_tool("TaskUpdate", {"taskId": "1", "status": "in_progress"},
                               "Starting the first task.")