Fix chat session picker agent switching (#81858)

* Fix chat session picker agent switching

Reset the chat session picker to the selected agent main session when switching agents and hide inactive sub-agent sessions from the normal picker options.

* fix(ui): preserve dashboard session on agent switch

Choose the most recent eligible normal/dashboard session for the selected agent while excluding subagent/internal rows; fall back to main only when no eligible session exists.

* fix(ui): avoid mutating session option sort

ui/src/ui/app-render.helpers.node.test.ts

@@ -534,10 +534,12 @@ describe("resolveSessionOptionGroups", () => {
     expect(labels).toEqual(["Subagent: cron-config-check"]);
   });
 
-  it("does not synthesize active grouped sessions without a listed row", () => {
+  it("keeps the active subagent session visible when no row exists yet", () => {
     const sessionKey = "agent:main:subagent:4f2146de-887b-4176-9abe-91140082959b";
 
-    expect(labelsForSessionOptions({ sessionKey })).toStrictEqual([]);
+    expect(labelsForSessionOptions({ sessionKey })).toEqual([
+      "subagent:4f2146de-887b-4176-9abe-91140082959b",
+    ]);
     expect(
       labelsForSessionOptions({
         sessionKey,
@@ -550,7 +552,7 @@ describe("resolveSessionOptionGroups", () => {
     expect(labelsForSessionOptions({ sessionKey: "agent:main:main" })).toEqual(["main"]);
   });
 
-  it("disambiguates duplicate grouped labels with scoped suffixes", () => {
+  it("hides inactive subagent sessions from the picker", () => {
     const labels = labelsForSessionOptions({
       sessionKey: "agent:main:subagent:4f2146de-887b-4176-9abe-91140082959b",
       sessions: [
@@ -565,10 +567,7 @@ describe("resolveSessionOptionGroups", () => {
       ],
     });
 
-    expect(labels).toEqual([
-      "Subagent: cron-config-check · subagent:4f2146de-887b-4176-9abe-91140082959b",
-      "Subagent: cron-config-check · subagent:6fb8b84b-c31f-410f-b7df-1553c82e43c9",
-    ]);
+    expect(labels).toEqual(["Subagent: cron-config-check"]);
   });
 
   it("filters the chat session options to the active agent", () => {
@@ -640,7 +639,7 @@ describe("resolveSessionOptionGroups", () => {
     expect(labels).toEqual(["Beta main"]);
   });
 
-  it("nests subagent sessions under their parent with visual prefix", () => {
+  it("hides spawned subagent sessions under their parent", () => {
     const parentKey = "agent:main:main";
     const subagentKey = "agent:main:subagent:4f2146de-887b-4176-9abe-91140082959b";
     const labels = labelsForSessionOptions({
@@ -651,24 +650,24 @@ describe("resolveSessionOptionGroups", () => {
       ],
     });
 
-    expect(labels).toEqual(["Spock", "└─ PLC Coder"]);
+    expect(labels).toEqual(["Spock"]);
   });
 
-  it("uses raw key fallback for subagent without label when nested", () => {
+  it("keeps the active subagent session visible without nesting it", () => {
     const parentKey = "agent:main:main";
     const subagentKey = "agent:main:subagent:f4ac7ef1-1234-5678-9abc-def012345678";
     const labels = labelsForSessionOptions({
-      sessionKey: parentKey,
+      sessionKey: subagentKey,
       sessions: [
         row({ key: parentKey, label: "Spock" }),
-        row({ key: subagentKey, spawnedBy: parentKey }),
+        row({ key: subagentKey, label: "PLC Coder", spawnedBy: parentKey }),
       ],
     });
 
-    expect(labels).toEqual(["Spock", "└─ f4ac7ef1-1234-5678-9abc-def012345678"]);
+    expect(labels).toEqual(["Spock", "Subagent: PLC Coder"]);
   });
 
-  it("preserves sibling row order when nesting subagent sessions", () => {
+  it("hides spawned subagent siblings regardless of row order", () => {
     const parentKey = "agent:main:main";
     const newerSubagentKey = "agent:main:subagent:newer";
     const olderSubagentKey = "agent:main:subagent:older";
@@ -681,7 +680,7 @@ describe("resolveSessionOptionGroups", () => {
       ],
     });
 
-    expect(labels).toEqual(["Spock", "└─ Newer", "└─ Older"]);
+    expect(labels).toEqual(["Spock"]);
   });
 });
 

ui/src/ui/chat/session-controls.ts

@@ -445,7 +445,6 @@ type SessionOptionEntry = {
   label: string;
   scopeLabel: string;
   title: string;
-  parentKey?: string;
 };
 
 export type SessionOptionGroup = {
@@ -478,22 +477,28 @@ function isAgentMainSessionKey(key: string): boolean {
 
 function resolvePreferredSessionForAgent(state: AppViewState, agentId: string): string {
   const normalizedAgentId = normalizeAgentId(agentId);
-  const defaultAgentId = normalizeAgentId(state.agentsList?.defaultId ?? "main");
-  const currentParsed = parseAgentSessionKey(state.sessionKey);
-  if (normalizeAgentId(currentParsed?.agentId ?? defaultAgentId) === normalizedAgentId) {
+  if (resolveChatAgentFilterId(state, state.sessionKey) === normalizedAgentId) {
     return state.sessionKey;
   }
-  const rows = state.sessionsResult?.sessions ?? [];
-  let row: (typeof rows)[number] | undefined;
-  for (const entry of rows) {
-    if (!isSessionKeyTiedToAgent(entry.key, normalizedAgentId, defaultAgentId)) {
-      continue;
-    }
-    if (!row || (entry.updatedAt ?? 0) > (row.updatedAt ?? 0)) {
-      row = entry;
-    }
+  const defaultAgentId = normalizeAgentId(state.agentsList?.defaultId ?? "main");
+  const eligible = (state.sessionsResult?.sessions ?? [])
+    .filter((row) => {
+      if (!isSessionKeyTiedToAgent(row.key, normalizedAgentId, defaultAgentId)) {
+        return false;
+      }
+      if (row.kind === "global" || row.kind === "unknown") {
+        return false;
+      }
+      if (isCronSessionKey(row.key)) {
+        return false;
+      }
+      return !isSubagentSessionKey(row.key) && !row.spawnedBy;
+    })
+    .toSorted((a, b) => (b.updatedAt ?? 0) - (a.updatedAt ?? 0));
+  if (eligible[0]?.key) {
+    return eligible[0].key;
   }
-  return row?.key ?? buildAgentMainSessionKey({ agentId: normalizedAgentId });
+  return buildAgentMainSessionKey({ agentId: normalizedAgentId });
 }
 
 function resolveChatAgentFilterOptions(state: AppViewState): ChatAgentFilterOption[] {
@@ -556,7 +561,7 @@ export function resolveSessionOptionGroups(
     return created;
   };
 
-  const addOption = (key: string, parentKey?: string, isChild?: boolean) => {
+  const addOption = (key: string) => {
     if (!key || seenKeys.has(key)) {
       return;
     }
@@ -570,16 +575,11 @@ export function resolveSessionOptionGroups(
         )
       : ensureGroup("other", "Other Sessions");
     const scopeLabel = normalizeOptionalString(parsed?.rest) ?? key;
-    let label = resolveSessionScopedOptionLabel(key, row, parsed?.rest);
-    if (isChild) {
-      label = `└─ ${label.replace(/^Subagent:\s*/i, "")}`;
-    }
     group.options.push({
       key,
-      label,
+      label: resolveSessionScopedOptionLabel(key, row, parsed?.rest),
       scopeLabel,
       title: key,
-      ...(parentKey ? { parentKey } : {}),
     });
   };
 
@@ -597,48 +597,17 @@ export function resolveSessionOptionGroups(
       continue;
     }
     const isSubagent = isSubagentSessionKey(row.key) || !!row.spawnedBy;
-    if (isSubagent && row.spawnedBy && byKey.has(row.spawnedBy)) {
-      addOption(row.key, row.spawnedBy, true);
-    } else {
-      addOption(row.key);
+    if (isSubagent && row.key !== sessionKey) {
+      continue;
     }
+    addOption(row.key);
   }
   if (byKey.has(sessionKey)) {
     addOption(sessionKey);
-  } else if (isAgentMainSessionKey(sessionKey)) {
+  } else if (isAgentMainSessionKey(sessionKey) || isSubagentSessionKey(sessionKey)) {
     addOption(sessionKey);
   }
 
-  for (const group of groups.values()) {
-    const options = group.options;
-    const optionKeys = new Set(options.map((option) => option.key));
-    const childrenByParent = new Map<string, SessionOptionEntry[]>();
-    for (const option of options) {
-      if (option.parentKey && optionKeys.has(option.parentKey)) {
-        const siblings = childrenByParent.get(option.parentKey);
-        if (siblings) {
-          siblings.push(option);
-        } else {
-          childrenByParent.set(option.parentKey, [option]);
-        }
-      }
-    }
-    if (childrenByParent.size > 0) {
-      const reordered: SessionOptionEntry[] = [];
-      for (const option of options) {
-        if (option.parentKey && optionKeys.has(option.parentKey)) {
-          continue;
-        }
-        reordered.push(option);
-        const children = childrenByParent.get(option.key);
-        if (children) {
-          reordered.push(...children);
-        }
-      }
-      options.splice(0, options.length, ...reordered);
-    }
-  }
-
   for (const group of groups.values()) {
     const counts = new Map<string, number>();
     for (const option of group.options) {

ui/src/ui/views/chat.test.ts

@@ -983,7 +983,7 @@ describe("chat session controls", () => {
     await i18n.setLocale("en");
   });
 
-  it("filters chat sessions by agent and switches to that agent's recent session", () => {
+  it("filters chat sessions by agent and switches to that agent's latest eligible session", () => {
     const { state } = createChatHeaderState();
     const onSwitchSession = vi.fn();
     state.sessionKey = "agent:alpha:main";
@@ -999,13 +999,25 @@ describe("chat session controls", () => {
     state.sessionsResult = {
       ts: 0,
       path: "",
-      count: 4,
+      count: 6,
       defaults: { modelProvider: "openai", model: "gpt-5", contextTokens: null },
       sessions: [
         { key: "agent:alpha:main", kind: "direct", updatedAt: 4 },
         { key: "agent:alpha:dashboard:alpha-recent", kind: "direct", updatedAt: 3 },
+        {
+          key: "agent:alpha:subagent:worker",
+          kind: "direct",
+          updatedAt: 5,
+          spawnedBy: "agent:alpha:main",
+        },
         { key: "agent:beta:dashboard:beta-recent", kind: "direct", updatedAt: 2 },
         { key: "agent:beta:main", kind: "direct", updatedAt: 1 },
+        {
+          key: "agent:beta:subagent:worker",
+          kind: "direct",
+          updatedAt: 6,
+          spawnedBy: "agent:beta:main",
+        },
       ],
     };