feat(maestro): force-kill prompt in the web client

The kill button now sends the unforced DELETE immediately instead of
asking first. Only the daemon's guard refusal raises a prompt, and it is
a real dialog rather than confirm(), so it can offer the override the
daemon already implements.

The API error envelope is decoded into ApiRequestError, keeping the code
and the unsaved-work breakdown so the dialog names what is in the way.

web/src/killDialog.ts

@@ -0,0 +1,104 @@
+/**
+ * Forced-kill prompt (#81).
+ *
+ * The daemon refuses to kill a session whose worktree still holds uncommitted
+ * or unpushed work. `confirm()` can only ask the same question twice, so the
+ * refusal gets its own dialog: it names what is in the way and offers the
+ * override the daemon's `force=true` already implements. A kill the daemon
+ * accepts never reaches here — there is nothing to warn about.
+ */
+import { formatInTheWay, type InTheWay } from "./types.js";
+
+export interface ForceKillPrompt {
+  /** Session name, as the sidebar shows it. */
+  name: string;
+  /** What the daemon reported in the way, when it reported anything. */
+  blockers: InTheWay | null;
+  /** Message from the daemon's refusal, shown when there is no breakdown. */
+  reason: string;
+  /** Run the forced kill. A rejection is rendered in the dialog, which stays
+   *  open so the override can be retried. */
+  onForce: () => Promise<void>;
+}
+
+let open: { el: HTMLElement; onKeydown: (ev: KeyboardEvent) => void } | null = null;
+
+export function closeForceKillDialog(): void {
+  if (!open) return;
+  window.removeEventListener("keydown", open.onKeydown, true);
+  open.el.remove();
+  open = null;
+}
+
+/** Mount the prompt. Opening while one is up replaces it, so a second refusal
+ *  can never stack two dialogs. */
+export function openForceKillDialog(p: ForceKillPrompt): HTMLElement {
+  closeForceKillDialog();
+
+  const el = document.createElement("div");
+  el.className = "kill-dialog";
+  el.setAttribute("role", "dialog");
+  el.setAttribute("aria-modal", "true");
+  el.setAttribute("aria-label", `Kill ${p.name}`);
+
+  const panel = document.createElement("div");
+  panel.className = "kill-dialog-panel";
+
+  const title = document.createElement("h2");
+  title.className = "kill-dialog-title";
+  title.textContent = `Kill "${p.name}"?`;
+
+  const body = document.createElement("p");
+  body.className = "kill-dialog-body";
+  body.textContent = p.blockers
+    ? `Its worktree still has ${formatInTheWay(p.blockers)}. Forcing the kill removes the session and leaves the worktree on disk.`
+    : `${p.reason} Forcing the kill removes the session and leaves the worktree on disk.`;
+
+  const error = document.createElement("p");
+  error.className = "kill-dialog-error";
+  error.hidden = true;
+
+  const actions = document.createElement("div");
+  actions.className = "kill-dialog-actions";
+  const cancel = document.createElement("button");
+  cancel.type = "button";
+  cancel.className = "btn btn-ghost kill-dialog-cancel";
+  cancel.textContent = "Cancel";
+  cancel.addEventListener("click", closeForceKillDialog);
+  const force = document.createElement("button");
+  force.type = "button";
+  force.className = "btn btn-danger kill-dialog-force";
+  force.textContent = "Force kill";
+  force.addEventListener("click", () => {
+    force.disabled = true;
+    void p
+      .onForce()
+      .then(closeForceKillDialog)
+      .catch((e: unknown) => {
+        force.disabled = false;
+        error.hidden = false;
+        error.textContent = `Failed to kill: ${(e as Error).message}`;
+      });
+  });
+  actions.append(cancel, force);
+
+  panel.append(title, body, error, actions);
+
+  // A press on the scrim cancels; one inside the panel is left alone.
+  el.addEventListener("click", (ev) => {
+    if (!panel.contains(ev.target as Node)) closeForceKillDialog();
+  });
+  el.appendChild(panel);
+  document.body.appendChild(el);
+
+  const onKeydown = (ev: KeyboardEvent): void => {
+    if (ev.key !== "Escape") return;
+    ev.preventDefault();
+    ev.stopPropagation();
+    closeForceKillDialog();
+  };
+  window.addEventListener("keydown", onKeydown, true);
+  open = { el, onKeydown };
+  cancel.focus();
+  return el;
+}