feat: post-review backlog hardening (cancel/parser/stall/history/9502)

Five independent items from the post-review backlog. F1: Stop on an external
agent task now aborts the running child via a per-task AbortController registry
reachable from the cancel route, and finalizes the assistant message as
cancelled (fixing two latent bugs — catch blocks left the message streaming,
and warm success-paths wrote complete on an aborted turn); warm pools/worktrees
are preserved and the native path is unchanged. F2/F3: prune the tool-call
parser to its two load-bearing exports (unexport eight zero-caller symbols, add
a gate test for the <invoke>-as-text fallback) and route placeholder-rejection
logging through pino. F6: a 90s per-chunk stall-timeout wraps native inference's
fullStream via AbortSignal.any so a hung stream finalizes the message instead of
hanging — no retry (a pure classifyStreamError helper is added). F7: a read-only
view_session_history MCP tool (newest-N, chronological). F9: retire the unused
apps/coder/web :9502 fallback SPA, keeping every API/WS/health/MCP route.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/components/ChatInput.tsx

@@ -49,6 +49,9 @@ interface Props {
   // queues while busy). Omitting onStop falls back to a (disabled) Send button.
   generating?: boolean;
   onStop?: () => void | Promise<void>;
+  // F1: disable the Stop button while a cancel request is already in flight, so a
+  // rapid second click can't fire a duplicate Stop. Optional — BooChat omits it.
+  stopDisabled?: boolean;
   // Batch 9.6: slash-command dispatch. When the input parses to a known skill,
   // ChatInput calls this with the skill name + the post-name args (possibly
   // empty). Callers wire this to api.chats.skillInvoke. Omitting the prop
@@ -76,7 +79,7 @@ interface Props {
   modelContextLimit?: number | null;
 }
 
-export function ChatInput({ disabled, projectId, agentId, onAgentChange, sessionId, webSearchEnabled, onSend, onForceSend, generating, onStop, onSlashCommand, slashGroups, chatId, chatLabel, messages, modelContextLimit }: Props) {
+export function ChatInput({ disabled, projectId, agentId, onAgentChange, sessionId, webSearchEnabled, onSend, onForceSend, generating, onStop, stopDisabled, onSlashCommand, slashGroups, chatId, chatLabel, messages, modelContextLimit }: Props) {
   const { isMobile } = useViewport();
   const [value, setValue] = useState('');
   const [busy, setBusy] = useState(false);
@@ -701,10 +704,11 @@ export function ChatInput({ disabled, projectId, agentId, onAgentChange, session
                 return (
                   <Button
                     onClick={() => void onStop()}
+                    disabled={stopDisabled}
                     size="icon"
                     variant="outline"
                     aria-label="Stop generating"
-                    title="Stop generating"
+                    title={stopDisabled ? 'Stopping…' : 'Stop generating'}
                   >
                     <Square className="fill-current size-3.5" />
                   </Button>