diff --git a/apps/backend/internal/agent/settings/store/sqlite.go b/apps/backend/internal/agent/settings/store/sqlite.go
index 7ebdf4ef69..d107159276 100644
--- a/apps/backend/internal/agent/settings/store/sqlite.go
+++ b/apps/backend/internal/agent/settings/store/sqlite.go
@@ -114,7 +114,7 @@ func (r *sqliteRepository) initSchema() error {
 }
 
 // migrateDropModelCheckConstraint recreates agent_profiles without the legacy
-// CHECK(model != '') constraint. Existing databases created before the ACP-first
+// CHECK(model != ”) constraint. Existing databases created before the ACP-first
 // migration carry this constraint, which prevents empty model values. New
 // databases (created by the CREATE TABLE IF NOT EXISTS above) never have it.
 //
diff --git a/apps/web/components/task/chat/chat-input-container.tsx b/apps/web/components/task/chat/chat-input-container.tsx
index 3de2ee165e..a25f8212c7 100644
--- a/apps/web/components/task/chat/chat-input-container.tsx
+++ b/apps/web/components/task/chat/chat-input-container.tsx
@@ -3,7 +3,9 @@
 import { forwardRef, useCallback, useState } from "react";
 import { IconAlertTriangle, IconPlus, IconPlayerPlay } from "@tabler/icons-react";
 import { Button } from "@kandev/ui/button";
+import { Tooltip, TooltipContent, TooltipTrigger } from "@kandev/ui/tooltip";
 import { NewSessionDialog } from "@/components/task/new-session-dialog";
+import { useAppStore } from "@/components/state-provider";
 import type { ContextFile } from "@/lib/state/context-files-store";
 import type { Message } from "@/lib/types/http";
 import type { DiffComment } from "@/lib/diff/types";
@@ -93,6 +95,15 @@ function FailedSessionBanner({
 }) {
   const [isResuming, setIsResuming] = useState(false);
 
+  const agentProfileId = useAppStore((s) =>
+    sessionId ? (s.taskSessions.items[sessionId]?.agent_profile_id ?? "") : "",
+  );
+  const profileExists = useAppStore(
+    (s) =>
+      agentProfileId !== "" &&
+      s.agentProfiles.items.some((p: { id: string }) => p.id === agentProfileId),
+  );
+
   const handleResume = useCallback(async () => {
     if (!sessionId || !taskId) return;
     const client = getWebSocketClient();
@@ -119,16 +130,24 @@ function FailedSessionBanner({
           </div>
           <div className="flex items-center gap-2">
             {sessionId && taskId && (
-              <Button
-                variant="default"
-                size="sm"
-                className="shrink-0 gap-1.5 cursor-pointer"
-                onClick={handleResume}
-                disabled={isResuming}
-              >
-                <IconPlayerPlay className="h-3.5 w-3.5" />
-                {isResuming ? "Resuming..." : "Resume"}
-              </Button>
+              <Tooltip>
+                <TooltipTrigger asChild>
+                  <span className="inline-flex" data-testid="failed-session-resume-wrapper">
+                    <Button
+                      variant="default"
+                      size="sm"
+                      data-testid="failed-session-resume-button"
+                      className="shrink-0 gap-1.5 cursor-pointer"
+                      onClick={handleResume}
+                      disabled={isResuming || !profileExists}
+                    >
+                      <IconPlayerPlay className="h-3.5 w-3.5" />
+                      {isResuming ? "Resuming..." : "Resume"}
+                    </Button>
+                  </span>
+                </TooltipTrigger>
+                {!profileExists && <TooltipContent>Agent profile no longer exists</TooltipContent>}
+              </Tooltip>
             )}
             <Button
               variant="outline"
diff --git a/apps/web/components/task/new-session-dialog.tsx b/apps/web/components/task/new-session-dialog.tsx
index 298e62dad1..0b3b050f7f 100644
--- a/apps/web/components/task/new-session-dialog.tsx
+++ b/apps/web/components/task/new-session-dialog.tsx
@@ -71,7 +71,22 @@ function useNewSessionDialogState(taskId: string) {
     return executor?.name ?? null;
   });
 
-  return { taskTitle, agentProfiles, currentSession, worktreeBranch, initialPrompt, executorLabel };
+  const sessionProfileId = currentSession?.agent_profile_id ?? "";
+  const profileIsValid = agentProfiles.some((p: { id: string }) => p.id === sessionProfileId);
+  const effectiveDefaultProfileId: string = profileIsValid
+    ? sessionProfileId
+    : (agentProfiles[0]?.id ?? "");
+
+  return {
+    taskTitle,
+    agentProfiles,
+    currentSession,
+    worktreeBranch,
+    initialPrompt,
+    executorLabel,
+    sessionProfileId,
+    effectiveDefaultProfileId,
+  };
 }
 
 function activateNewSession(
@@ -111,6 +126,7 @@ function useSessionOptions(taskId: string) {
 function NewSessionForm({
   taskId,
   defaultProfileId,
+  initialProfileId,
   executorId,
   executorLabel,
   worktreeBranch,
@@ -121,6 +137,7 @@ function NewSessionForm({
 }: {
   taskId: string;
   defaultProfileId: string;
+  initialProfileId?: string;
   executorId: string;
   executorLabel: string | null;
   worktreeBranch: string | null;
@@ -134,7 +151,7 @@ function NewSessionForm({
   const { summarize, isSummarizing } = useSummarizeSession();
   const [isCreating, setIsCreating] = useState(false);
   const [contextValue, setContextValue] = useState("blank");
-  const [selectedProfileId, setSelectedProfileId] = useState(defaultProfileId);
+  const [selectedProfileId, setSelectedProfileId] = useState(initialProfileId ?? defaultProfileId);
   const [hasPrompt, setHasPrompt] = useState(false);
   const promptRef = useRef<HTMLTextAreaElement>(null);
   const {
@@ -167,6 +184,12 @@ function NewSessionForm({
       }
     });
   }, [enhancePrompt]);
+  const hasProfiles = profileOptions.length > 0;
+  const showAgentSelector =
+    hasProfiles &&
+    (profileOptions.length > 1 ||
+      (!!defaultProfileId && !profileOptions.find((o) => o.value === defaultProfileId)));
+  const isBusy = isCreating || isSummarizing;
 
   const handleContextChange = useCallback(
     async (value: string) => {
@@ -207,7 +230,7 @@ function NewSessionForm({
       if (!prompt) return;
       setIsCreating(true);
       try {
-        const { request } = buildStartRequest(taskId, selectedProfileId || defaultProfileId, {
+        const { request } = buildStartRequest(taskId, selectedProfileId, {
           executorId,
           prompt,
           attachments: toMessageAttachments(attachments),
@@ -216,9 +239,7 @@ function NewSessionForm({
         if (!response.session_id) {
           throw new Error("Session created but no session ID returned");
         }
-        const profile = agentProfiles.find(
-          (p: AgentProfileOption) => p.id === (selectedProfileId || defaultProfileId),
-        );
+        const profile = agentProfiles.find((p: AgentProfileOption) => p.id === selectedProfileId);
         activateNewSession(
           response.session_id,
           taskId,
@@ -240,7 +261,6 @@ function NewSessionForm({
     [
       taskId,
       selectedProfileId,
-      defaultProfileId,
       executorId,
       contextValue,
       initialPrompt,
@@ -253,17 +273,20 @@ function NewSessionForm({
     ],
   );
 
-  const showSessions = sessionOptions;
-
   return (
     <form onSubmit={handleSubmit} className="space-y-4">
       <EnvironmentBadges executorLabel={executorLabel} worktreeBranch={worktreeBranch} />
-      {profileOptions.length > 1 && (
+      {!hasProfiles && (
+        <p className="text-xs text-center text-muted-foreground">
+          No agent profiles configured. Add one in Settings → Agents first.
+        </p>
+      )}
+      {showAgentSelector && (
         <div className="space-y-1.5">
           <label className="text-xs font-medium text-muted-foreground">Agent Profile</label>
           <AgentSelector
             options={profileOptions}
-            value={selectedProfileId || defaultProfileId}
+            value={selectedProfileId}
             onValueChange={setSelectedProfileId}
             disabled={isCreating}
             placeholder="Select agent profile"
@@ -274,7 +297,7 @@ function NewSessionForm({
         value={contextValue}
         onValueChange={handleContextChange}
         hasInitialPrompt={!!initialPrompt}
-        sessionOptions={showSessions}
+        sessionOptions={sessionOptions}
         isSummarizing={isSummarizing}
       />
       <div
@@ -290,18 +313,24 @@ function NewSessionForm({
             placeholder="What should the agent work on?"
             className="border-0 focus-visible:ring-0 focus-visible:ring-offset-0 min-h-[120px] max-h-[240px] resize-none overflow-auto text-[13px]"
             autoFocus
-            disabled={isCreating || isSummarizing}
+            disabled={isBusy}
             onInput={(e) => setHasPrompt(!!e.currentTarget.value)}
             onPaste={handlePaste}
             onKeyDown={(e) => {
-              if (e.key === "Enter" && (e.metaKey || e.ctrlKey)) {
+              if (
+                e.key === "Enter" &&
+                (e.metaKey || e.ctrlKey) &&
+                !isBusy &&
+                hasPrompt &&
+                hasProfiles
+              ) {
                 e.preventDefault();
                 handleSubmit(e);
               }
             }}
           />
           <div className="flex items-center px-1 pb-1">
-            <AttachButton onClick={handleAttachClick} disabled={isCreating || isSummarizing} />
+            <AttachButton onClick={handleAttachClick} disabled={isBusy} />
             <EnhancePromptButton
               onClick={handleEnhancePrompt}
               isLoading={isEnhancingPrompt}
@@ -343,7 +372,7 @@ function NewSessionForm({
         </Button>
         <Button
           type="submit"
-          disabled={isCreating || isSummarizing || !hasPrompt}
+          disabled={isBusy || !hasPrompt || !hasProfiles}
           className="cursor-pointer"
         >
           {isCreating ? "Creating..." : "Start Agent"}
@@ -354,8 +383,16 @@ function NewSessionForm({
 }
 
 export function NewSessionDialog({ open, onOpenChange, taskId, groupId }: NewSessionDialogProps) {
-  const { taskTitle, agentProfiles, currentSession, worktreeBranch, initialPrompt, executorLabel } =
-    useNewSessionDialogState(taskId);
+  const {
+    taskTitle,
+    agentProfiles,
+    currentSession,
+    worktreeBranch,
+    initialPrompt,
+    executorLabel,
+    sessionProfileId,
+    effectiveDefaultProfileId,
+  } = useNewSessionDialogState(taskId);
 
   return (
     <Dialog open={open} onOpenChange={onOpenChange}>
@@ -368,7 +405,8 @@ export function NewSessionDialog({ open, onOpenChange, taskId, groupId }: NewSes
         <NewSessionForm
           key={`${open}`}
           taskId={taskId}
-          defaultProfileId={currentSession?.agent_profile_id ?? ""}
+          defaultProfileId={sessionProfileId}
+          initialProfileId={effectiveDefaultProfileId}
           executorId={currentSession?.executor_id ?? ""}
           executorLabel={executorLabel}
           worktreeBranch={worktreeBranch}
diff --git a/apps/web/e2e/pages/session-page.ts b/apps/web/e2e/pages/session-page.ts
index f6a067c094..be96f65baf 100644
--- a/apps/web/e2e/pages/session-page.ts
+++ b/apps/web/e2e/pages/session-page.ts
@@ -61,6 +61,18 @@ export class SessionPage {
   todoIndicator() {
     return this.page.getByTestId("todo-indicator");
   }
+  /** Resume button shown in the FailedSessionBanner. */
+  failedSessionResumeButton(): Locator {
+    return this.page.getByTestId("failed-session-resume-button");
+  }
+  /** Span wrapper around the resume button — used to trigger tooltip on disabled state. */
+  failedSessionResumeWrapper(): Locator {
+    return this.page.getByTestId("failed-session-resume-wrapper");
+  }
+  /** Cancel button shown in the chat toolbar while an agent turn is running. */
+  cancelAgentButton(): Locator {
+    return this.page.getByTestId("cancel-agent-button");
+  }
 
   async waitForLoad(timeout = 15_000) {
     // When multiple session tabs are open, multiple session-chat panels exist in
@@ -550,6 +562,12 @@ export class SessionPage {
     await tab.click({ button: "right" });
   }
 
+  /** Right-click the first session tab (useful when there is only one session). */
+  async rightClickFirstSessionTab(): Promise<void> {
+    const tab = this.page.locator("[data-testid^='session-tab-']").first();
+    await tab.click({ button: "right" });
+  }
+
   /** Context menu item by visible label. */
   contextMenuItem(label: string): Locator {
     return this.page.getByRole("menuitem", { name: label });
diff --git a/apps/web/e2e/tests/session/new-session-deleted-profile.spec.ts b/apps/web/e2e/tests/session/new-session-deleted-profile.spec.ts
new file mode 100644
index 0000000000..c66e898e30
--- /dev/null
+++ b/apps/web/e2e/tests/session/new-session-deleted-profile.spec.ts
@@ -0,0 +1,159 @@
+import { test, expect } from "../../fixtures/test-base";
+import { KanbanPage } from "../../pages/kanban-page";
+import { SessionPage } from "../../pages/session-page";
+
+/** Navigate to a kanban card by title and open its session page. */
+async function openTaskSession(page: Parameters<typeof KanbanPage>[0], title: string) {
+  const kanban = new KanbanPage(page);
+  await kanban.goto();
+
+  const card = kanban.taskCardByTitle(title);
+  await expect(card).toBeVisible({ timeout: 15_000 });
+  await card.click();
+  await expect(page).toHaveURL(/\/t\//, { timeout: 15_000 });
+
+  const session = new SessionPage(page);
+  await session.waitForLoad();
+
+  // Reload to get fresh SSR state — the session may have started via API before
+  // the WS connection was established, causing the UI to miss "session is RUNNING"
+  // events. A reload guarantees hydrated state from the server.
+  await page.reload();
+  await session.waitForLoad();
+
+  return session;
+}
+
+/**
+ * Stop the running session via the tab context menu (session.stop → CANCELLED state),
+ * then wait for the FailedSessionBanner to appear.
+ *
+ * Note: clicking the cancel-agent-button sends `agent.cancel` which only cancels
+ * the current turn and transitions to WAITING_FOR_INPUT (not CANCELLED/FAILED).
+ * To reach CANCELLED we need `session.stop` which is triggered via right-click → Stop.
+ */
+async function stopRunningSession(session: SessionPage) {
+  // Wait for the agent to be actively running (cancel button becomes visible)
+  await expect(session.cancelAgentButton()).toBeVisible({ timeout: 30_000 });
+
+  // Right-click the session tab to open context menu, then click "Stop"
+  // This sends session.stop → CANCELLED state
+  await session.rightClickFirstSessionTab();
+  await session.contextMenuItem("Stop").click();
+
+  // Wait for the FailedSessionBanner's resume button to appear (isFailed = FAILED | CANCELLED)
+  await expect(session.failedSessionResumeButton()).toBeVisible({ timeout: 30_000 });
+}
+
+test.describe("New session with deleted agent profile", () => {
+  test("resume button is disabled when agent profile was deleted", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(90_000);
+
+    // 1. Get agent info and create a temporary custom profile
+    const { agents } = await apiClient.listAgents();
+    const agent = agents[0];
+    if (!agent) throw new Error("No agents available");
+    const profile = await apiClient.createAgentProfile(agent.id, "Temp Profile for Delete Test", {
+      model: agent.profiles[0]?.model ?? "mock",
+      auto_approve: true,
+    });
+
+    // 2. Create task using the custom profile with a slow response so we can cancel it
+    await apiClient.createTaskWithAgent(
+      seedData.workspaceId,
+      "Deleted Profile Resume Test",
+      profile.id,
+      {
+        description: "/slow 60s",
+        workflow_id: seedData.workflowId,
+        workflow_step_id: seedData.startStepId,
+        repository_ids: [seedData.repositoryId],
+      },
+    );
+
+    // 3. Navigate to the task and stop the agent to get CANCELLED state
+    const session = await openTaskSession(testPage, "Deleted Profile Resume Test");
+    await stopRunningSession(session);
+
+    // 4. While on the page, force-delete the custom agent profile.
+    //    The frontend receives an "agent.profile.deleted" WS event and removes
+    //    the profile from the store, making profileExists=false reactively.
+    await apiClient.deleteAgentProfile(profile.id, true);
+
+    // 5. Wait for the resume button to become disabled (store has updated)
+    await expect(session.failedSessionResumeButton()).toBeDisabled({ timeout: 10_000 });
+
+    // 6. Hover the span wrapper (tooltip trigger) and verify the tooltip text
+    await testPage.getByTestId("failed-session-resume-wrapper").hover();
+    await expect(testPage.getByRole("tooltip")).toContainText("Agent profile no longer exists", {
+      timeout: 5_000,
+    });
+  });
+
+  test("new agent dialog falls back to available profile when original was deleted", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(120_000);
+
+    // 1. Get agent info and create a temporary custom profile
+    const { agents } = await apiClient.listAgents();
+    const agent = agents[0];
+    if (!agent) throw new Error("No agents available");
+    const profile = await apiClient.createAgentProfile(agent.id, "Temp Profile for Dialog Test", {
+      model: agent.profiles[0]?.model ?? "mock",
+      auto_approve: true,
+    });
+
+    // 2. Create task using the custom profile with a slow response so we can cancel it
+    await apiClient.createTaskWithAgent(
+      seedData.workspaceId,
+      "Deleted Profile Dialog Test",
+      profile.id,
+      {
+        description: "/slow 60s",
+        workflow_id: seedData.workflowId,
+        workflow_step_id: seedData.startStepId,
+        repository_ids: [seedData.repositoryId],
+      },
+    );
+
+    // 3. Navigate to the task and stop the agent to get CANCELLED state
+    const session = await openTaskSession(testPage, "Deleted Profile Dialog Test");
+    await stopRunningSession(session);
+
+    // 4. While on the page, force-delete the custom agent profile.
+    //    The frontend receives an "agent.profile.deleted" WS event and removes
+    //    the profile from the store.
+    await apiClient.deleteAgentProfile(profile.id, true);
+
+    // 5. Wait for the resume button to become disabled (confirms store updated)
+    await expect(session.failedSessionResumeButton()).toBeDisabled({ timeout: 10_000 });
+
+    // 6. Click the "New Agent" button in the FailedSessionBanner to open the dialog
+    await testPage.getByRole("button", { name: "New Agent" }).click();
+
+    // 7. Dialog should be visible
+    await expect(session.newSessionDialog()).toBeVisible({ timeout: 5_000 });
+
+    // 8. Agent selector should be visible because the original profile was deleted
+    //    (isDefaultProfileMissing=true forces the selector to show even with 1 profile)
+    const agentSelector = session.newSessionDialog().getByTestId("agent-profile-selector");
+    await expect(agentSelector).toBeVisible();
+
+    // 9. Fill in a prompt and submit to create a new session with the fallback profile
+    await session.newSessionPromptInput().fill("/e2e:simple-message");
+    await session.newSessionStartButton().click();
+
+    // 10. Dialog should close after submit
+    await expect(session.newSessionDialog()).not.toBeVisible({ timeout: 10_000 });
+
+    // 11. Verify the new session tab is visible
+    await expect(session.sessionTabByText("2")).toBeVisible({ timeout: 15_000 });
+  });
+});