Claude proxy: an Esc mid-stream never ends the flow, so the phase stays busy (stuck Thinking, goal-loop Resume) #1040

Found by the #1028 re-review. The review read the mitmproxy 12.2.2 source and reproduced the shape with probes.

What happens

When the user presses Esc while Claude is streaming, Claude Code closes the HTTP connection.

• mitmproxy: it reports a client disconnect only through its error hook. _http1.py wait() raises RequestProtocolError("Client disconnected."), which goes to handle_protocol_error. The end-of-stream call the addon turns into response-end runs only on a normal end of message (http/__init__.py:460-462).
• Our addon: mitmAddon.py (claude-code-headless) has no error hook, so nothing is emitted.
• The adapter: ClaudeProxyAdapter.handleTransportEvent never reaches onEnd. The stream phase stays at the last working phase (thinking, responding, tool-input, or requesting if the Esc came before the first chunk).
• What resets it: only the next flow's first chunk (if the old flow is more than 30 s stale) or sealFlowsSilentSince after a machine sleep.

Effects

• The feed can keep showing a working phase ("Thinking") after an Esc until the next prompt.
• Goal loop (fix(goal-loop): continue on the provider's Stop hook, never on stream phases #1028): a turn that ended with Esc has no Stop hook, and its phase never goes idle, so Resume cannot close it. Only a typed prompt recovers the loop. This is pinned as a known limit in GoalLoopService.test.ts.

Fix

• In mitmAddon.py, add an error(flow) hook that emits a terminal transport event for the flow.
• In ClaudeProxyAdapter, seal that flow and publish idle for it when it owns the phase.
• Test: a recorded or captured disconnect sequence, through the real adapter.

Related: the planned adapter change that classifies cc_is_subagent flows before first-chunk promotion. It also removes the subagent demotion idle edge (#1024, and the re-review's probe H).