fix(web): stabilize useMutation results so TerminalPanel stops flooding /shell/resize

The mutationFn / onSuccess closures inside every useMutation in
process.ts were created fresh on every render, which made the
mutation result object unstable across renders. TerminalPanel's
terminal-init useEffect has [resize, workspaceId] as deps; with
"resize" changing on every render, the effect re-ran on every
render, which:
  - disposed and recreated the xterm Terminal
  - re-attached onResize (which fires fit() → onResize → mutate)
  - 100ms debounce kept getting reset
  - but the effect re-creating itself with new closures every
    ~16ms kept fit()'s pre-resize state oscillating, eventually
    letting the debounce expire and firing the API
Result: /api/workspaces/:id/shell/resize was being spammed.

Fix: wrap every useMutation's mutationFn (and onSuccess where
present) in useCallback with explicit deps. useMutation now sees a
stable config and returns a stable result object. The terminal
effect's dep [resize, workspaceId] no longer changes per render
unless workspaceId actually changes.

Affects: useProcessStart/Stop/Restart, useShellStart/Stop/
Restart/Resize. All same pattern, all same risk.

web/src/lib/api/process.ts

@@ -188,14 +188,19 @@ function useProcessActionMutation(
   action: "start" | "stop" | "restart",
 ): UseMutationResult<void, Error, string> {
   const queryClient = useQueryClient();
-  return useMutation({
-    mutationFn: (workspaceId: string) => postProcessAction(workspaceId, action),
-    onSuccess: (_, workspaceId) => {
+  const mutationFn = useCallback(
+    (workspaceId: string) => postProcessAction(workspaceId, action),
+    [action],
+  );
+  const onSuccess = useCallback(
+    (_: void, workspaceId: string) => {
       queryClient.invalidateQueries({
         queryKey: processStatusQueryKey(workspaceId),
       });
     },
-  });
+    [queryClient],
+  );
+  return useMutation({ mutationFn, onSuccess });
 }
 
 
@@ -215,69 +220,72 @@ export function useShellStart(
   workspaceId: string | null,
 ): UseMutationResult<ShellInfo, Error, void> {
   const queryClient = useQueryClient();
-  return useMutation({
-    mutationFn: async () => {
-      if (!workspaceId) {
-        throw new Error("workspace id required");
-      }
-      return postShellStart(workspaceId);
-    },
-    onSuccess: () => {
-      if (!workspaceId) return;
-      queryClient.invalidateQueries({
-        queryKey: shellListQueryKey(workspaceId),
-      });
-      queryClient.invalidateQueries({
-        queryKey: ["workspaces", workspaceId, "shell", "status"],
-      });
-    },
-  });
+  const mutationFn = useCallback(async () => {
+    if (!workspaceId) {
+      throw new Error("workspace id required");
+    }
+    return postShellStart(workspaceId);
+  }, [workspaceId]);
+  const onSuccess = useCallback(() => {
+    if (!workspaceId) return;
+    queryClient.invalidateQueries({
+      queryKey: shellListQueryKey(workspaceId),
+    });
+    queryClient.invalidateQueries({
+      queryKey: ["workspaces", workspaceId, "shell", "status"],
+    });
+  }, [queryClient, workspaceId]);
+  return useMutation({ mutationFn, onSuccess });
 }
 
 export function useShellStop(
   workspaceId: string | null,
 ): UseMutationResult<void, Error, { shellId: string }> {
   const queryClient = useQueryClient();
-  return useMutation({
-    mutationFn: async ({ shellId }) => {
+  const mutationFn = useCallback(
+    async ({ shellId }: { shellId: string }) => {
       if (!workspaceId) {
         throw new Error("workspace id required");
       }
       return postShellStop(workspaceId, shellId);
     },
-    onSuccess: () => {
-      if (!workspaceId) return;
-      queryClient.invalidateQueries({
-        queryKey: shellListQueryKey(workspaceId),
-      });
-      queryClient.invalidateQueries({
-        queryKey: ["workspaces", workspaceId, "shell", "status"],
-      });
-    },
-  });
+    [workspaceId],
+  );
+  const onSuccess = useCallback(() => {
+    if (!workspaceId) return;
+    queryClient.invalidateQueries({
+      queryKey: shellListQueryKey(workspaceId),
+    });
+    queryClient.invalidateQueries({
+      queryKey: ["workspaces", workspaceId, "shell", "status"],
+    });
+  }, [queryClient, workspaceId]);
+  return useMutation({ mutationFn, onSuccess });
 }
 
 export function useShellRestart(
   workspaceId: string | null,
 ): UseMutationResult<ShellInfo, Error, { shellId: string }> {
   const queryClient = useQueryClient();
-  return useMutation({
-    mutationFn: async ({ shellId }) => {
+  const mutationFn = useCallback(
+    async ({ shellId }: { shellId: string }) => {
       if (!workspaceId) {
         throw new Error("workspace id required");
       }
       return postShellRestart(workspaceId, shellId);
     },
-    onSuccess: () => {
-      if (!workspaceId) return;
-      queryClient.invalidateQueries({
-        queryKey: shellListQueryKey(workspaceId),
-      });
-      queryClient.invalidateQueries({
-        queryKey: ["workspaces", workspaceId, "shell", "status"],
-      });
-    },
-  });
+    [workspaceId],
+  );
+  const onSuccess = useCallback(() => {
+    if (!workspaceId) return;
+    queryClient.invalidateQueries({
+      queryKey: shellListQueryKey(workspaceId),
+    });
+    queryClient.invalidateQueries({
+      queryKey: ["workspaces", workspaceId, "shell", "status"],
+    });
+  }, [queryClient, workspaceId]);
+  return useMutation({ mutationFn, onSuccess });
 }
 
 async function postShellResize(
@@ -303,14 +311,21 @@ export function useShellResize(
   workspaceId: string | null,
   shellId: string | null,
 ): UseMutationResult<void, Error, { cols: number; rows: number }> {
-  return useMutation({
-    mutationFn: async ({ cols, rows }) => {
+  // Stable mutationFn: without useCallback, a fresh closure is created on
+  // every render, which makes useMutation's returned object unstable. That
+  // ripples into useEffect dep arrays in TerminalPanel and causes the
+  // terminal to be torn down and recreated on every render — which fires
+  // onResize in a tight loop and floods /shell/resize.
+  const mutationFn = useCallback(
+    async ({ cols, rows }: { cols: number; rows: number }) => {
       if (!workspaceId || !shellId) {
         throw new Error("workspace id and shell id required");
       }
       return postShellResize(workspaceId, shellId, cols, rows);
     },
-  });
+    [workspaceId, shellId],
+  );
+  return useMutation({ mutationFn });
 }
 
 export type ProcessWebSocketStatus =