Handoff-style /model switch command and per-turn thinking level (#64)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/web/test/agent-mentions.test.ts

@@ -1,8 +1,9 @@
 /**
  * agent-mentions.ts unit tests: @ mention matching (cursor prefix / boundary
  * rules), candidate filtering, send-time parsing of a leading @ mention,
- * generation of the first new-conversation <handoff_from> origin block, and
- * <scheduled_task> origin block parsing.
+ * generation of the first new-conversation <handoff_from> origin block,
+ * <scheduled_task> origin block parsing, and the /model switch's
+ * <model_switch_from> origin block round-trip.
  */
 import { describe, expect, it } from "vitest";
 import type { AgentSummary } from "@prismshadow/penguin-server/api";
@@ -10,7 +11,9 @@ import {
   filterAgents,
   handoffMessage,
   matchMention,
+  modelSwitchMessage,
   parseHandoffMessage,
+  parseModelSwitchMessage,
   parseScheduledMessage,
   splitLeadingMention,
 } from "../src/features/chat/agent-mentions";
@@ -212,3 +215,37 @@ describe("parseScheduledMessage (parses the scheduled-task origin block, driving
     ).toBeNull();
   });
 });
+
+describe("modelSwitchMessage / parseModelSwitchMessage (the /model switch origin block)", () => {
+  it("round-trips a full origin (session title with parentheses, trace path, workspace, previous pair)", () => {
+    const origin = {
+      sessionId: "session-2026-07-24-10-00-00-abcdef01",
+      sessionTitle: "Fix (the) parser",
+      tracePath: "/data/p/agents/a/traces/2026-07-24/session-x_001.jsonl",
+      workspace: "/data/ws",
+      prevProvider: "deepseek",
+      prevModelId: "deepseek-v4-pro",
+    };
+    expect(parseModelSwitchMessage(modelSwitchMessage(origin))).toEqual(origin);
+  });
+
+  it("minimal origin (session id only) round-trips; optional lines are omitted from the block", () => {
+    const text = modelSwitchMessage({ sessionId: "session-01" });
+    expect(text).not.toContain("trace:");
+    expect(text).not.toContain("workspace:");
+    expect(text).not.toContain("previous_model:");
+    expect(parseModelSwitchMessage(text)).toEqual({ sessionId: "session-01" });
+  });
+
+  it("plain messages and longer messages merely containing the block are not misdetected", () => {
+    expect(parseModelSwitchMessage("hello /model")).toBeNull();
+    expect(
+      parseModelSwitchMessage(`before\n${modelSwitchMessage({ sessionId: "s1" })}`),
+    ).toBeNull();
+    expect(parseModelSwitchMessage(`${modelSwitchMessage({ sessionId: "s1" })}\nafter`)).toBeNull();
+    // A block without a session line is not an origin block.
+    expect(
+      parseModelSwitchMessage("<model_switch_from>\ntrace: /t.jsonl\n</model_switch_from>"),
+    ).toBeNull();
+  });
+});

packages/web/test/stream-model.test.ts

@@ -77,7 +77,6 @@ function meta(sessionId: string): OmniMessage<SessionMetaPayload> {
     model_context_window: 200000,
     system_prompt: "",
     tools: [],
-    thinking_level: "default",
     agent_state: "/a",
     workspace: "/w",
   });
@@ -279,34 +278,6 @@ describe("approvals and events", () => {
     expect(items(m)).toHaveLength(0);
   });
 
-  it("captures the session's thinking level from the main session_meta (read-only input-area tag)", () => {
-    const m = createStreamModel();
-    expect(m.thinkingLevel).toBeNull();
-    // The shared helper's meta carries thinking_level "default" (Agent config leaves it unset).
-    pushMessage(m, meta("session-x"));
-    expect(m.thinkingLevel).toBe("default");
-
-    const m2 = createStreamModel();
-    pushMessage(
-      m2,
-      sessionMeta({
-        session_id: "session-y",
-        model_id: "m",
-        provider: "custom",
-        model_context_window: 200000,
-        system_prompt: "",
-        tools: [],
-        thinking_level: "medium",
-        agent_state: "/a",
-        workspace: "/w",
-      }),
-    );
-    expect(m2.thinkingLevel).toBe("medium");
-    // An origin-tagged (sub-session) session_meta routes to the nested model and must not clobber the main session's level.
-    pushMessage(m2, withOrigin(meta("child"), "child"));
-    expect(m2.thinkingLevel).toBe("medium");
-  });
-
   it("request_end final state timeout/malformed produces a retry notice item (with attempt number); request_begin marks it as resent", () => {
     const m = createStreamModel();
     pushMessage(m, requestBegin());

packages/web/test/thinking-level.test.ts

@@ -1,8 +1,10 @@
 /**
- * thinking-level.ts unit tests: the conversation-time picker's short-name lookup and the
- * selectable list — the picker offers only low/medium/high/xhigh (many models cannot disable
- * thinking), while "none" stays a displayable stored value; "" (no override yet) and
- * session_meta's "default" resolve to null (trigger shows a placeholder; the session tag hides).
+ * thinking-level.ts unit tests: the conversation-time pickers' short-name lookup and the
+ * selectable list — both pickers offer only low/medium/high/xhigh (many models cannot disable
+ * thinking; there is no "follow config" row — the session picker auto-follows the Agent
+ * config by initializing its display to it), while "none" stays a displayable stored value;
+ * "" (internally "untouched"/no override) and a legacy meta's "default" resolve to null so
+ * callers substitute the config level or a placeholder.
  */
 import { describe, expect, it } from "vitest";
 import {
@@ -40,7 +42,7 @@ describe("thinking level lists", () => {
 });
 
 describe("thinkingLevelLabel", () => {
-  it("returns null for non-levels: '' (no override yet), session_meta's 'default', unknown, null", () => {
+  it("returns null for non-levels: '' (untouched/no override), a legacy meta's 'default', unknown, null", () => {
     expect(thinkingLevelLabel(NAMES, "")).toBeNull();
     expect(thinkingLevelLabel(NAMES, "default")).toBeNull();
     expect(thinkingLevelLabel(NAMES, "ultra")).toBeNull();