diff --git a/electron/services-threads.js b/electron/services-threads.js
index ee634b33c..20845b244 100644
--- a/electron/services-threads.js
+++ b/electron/services-threads.js
@@ -538,7 +538,7 @@ function setProvider(store, input) {
   const providerChanging =
     providerProvided && String(input.provider) !== String(thread.provider);
 
-  /** @type {{ provider?: string, model?: string | null, sessionId?: null, reasoningEffort?: null, webSearch?: boolean }} */
+  /** @type {{ provider?: string, model?: string | null, sessionId?: null, replayContext?: boolean, reasoningEffort?: null, webSearch?: boolean }} */
   const patch = {};
 
   if (providerChanging && thread.status === "working") {
@@ -612,6 +612,13 @@ function setProvider(store, input) {
     }
   }
 
+  if (patch.sessionId === null) {
+    // The new CLI (or re-pinned model) starts with no memory of this thread.
+    // Replay its own retained tail on the next send, same as a rewind (#254),
+    // or a switch mid-task (and quota failover) restarts blind (#1493).
+    patch.replayContext = true;
+  }
+
   const updated = store.updateThread(threadId, patch);
   store.save();
   const row = updated || { ...thread, ...patch };
diff --git a/electron/store.js b/electron/store.js
index a3bcd7363..6a27fab4a 100644
--- a/electron/store.js
+++ b/electron/store.js
@@ -2352,6 +2352,9 @@ class Store {
         !Object.prototype.hasOwnProperty.call(patch, "sessionId")
       ) {
         p = { ...patch, sessionId: null };
+        // Same rule as setProvider (#1493): a dropped session replays the
+        // thread's own tail so the next turn is not blind.
+        if (t.sessionId) p.replayContext = true;
       }
       // Snapshot the rollout model on first sessionId (or a replacement
       // id). Codex exec resume ignores later picker changes (#1215).
diff --git a/electron/test/provider-switch-context.test.js b/electron/test/provider-switch-context.test.js
new file mode 100644
index 000000000..b071f1262
--- /dev/null
+++ b/electron/test/provider-switch-context.test.js
@@ -0,0 +1,232 @@
+"use strict";
+
+/**
+ * Issue #1493: a provider switch (manual or quota failover) drops the old
+ * CLI's session, so the next run must replay the thread's own tail instead
+ * of starting with no history.
+ */
+
+const { describe, it, beforeEach, afterEach } = require("node:test");
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+const { pathToFileURL } = require("node:url");
+const { execFileSync } = require("node:child_process");
+const { Store } = require("../store.js");
+const services = require("../services.js");
+const { getProvider } = require("../providers.js");
+const { createRunner } = require("../runner.js");
+const { rmTree } = require("./support/rmTree.js");
+
+function git(cwd, args) {
+  execFileSync("git", args, { cwd, stdio: "ignore" });
+}
+
+async function loadCore() {
+  const corePath = path.join(__dirname, "../../core/dist/index.js");
+  return import(pathToFileURL(corePath).href);
+}
+
+function waitFor(predicate, { timeoutMs = 15000, intervalMs = 20 } = {}) {
+  return new Promise((resolve, reject) => {
+    const start = Date.now();
+    const tick = () => {
+      try {
+        if (predicate()) return resolve();
+      } catch (e) {
+        return reject(e);
+      }
+      if (Date.now() - start > timeoutMs) {
+        return reject(new Error("waitFor timed out"));
+      }
+      setTimeout(tick, intervalMs);
+    };
+    tick();
+  });
+}
+
+/**
+ * Generic agent (CODER_AGENT_CMD gets the prompt as its last argv): logs each
+ * prompt as a JSON line, fails the first call with `firstError` when given.
+ * Hex + eval because parseAgentCommand splits on spaces.
+ */
+function agentCmd(logFile, firstError) {
+  const src = `
+const fs = require("fs");
+const log = ${JSON.stringify(logFile)};
+const first = !fs.existsSync(log);
+fs.appendFileSync(log, JSON.stringify(process.argv[process.argv.length - 1]) + "\\n");
+if (first && ${JSON.stringify(firstError || "")}) {
+  process.stderr.write(${JSON.stringify(firstError || "")});
+  process.exit(1);
+}
+process.stdout.write("ok");
+`;
+  const hex = Buffer.from(src, "utf8").toString("hex");
+  return `${process.execPath} -e eval(Buffer.from('${hex}','hex').toString())`;
+}
+
+function readPrompts(logFile) {
+  return fs
+    .readFileSync(logFile, "utf8")
+    .trim()
+    .split("\n")
+    .map((l) => JSON.parse(l));
+}
+
+describe("provider switch keeps context (#1493)", () => {
+  let tmpDir;
+  let store;
+  let runner;
+  let project;
+  let logFile;
+  let prevSimulate;
+  let prevAgentCmd;
+
+  beforeEach(async () => {
+    prevSimulate = process.env.CODER_SIMULATE;
+    prevAgentCmd = process.env.CODER_AGENT_CMD;
+    delete process.env.CODER_SIMULATE;
+
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "coder-switch-ctx-"));
+    logFile = path.join(tmpDir, "prompts.jsonl");
+    store = new Store(path.join(tmpDir, "store.json"));
+    runner = createRunner({
+      store,
+      core: await loadCore(),
+      pushFn: () => {},
+      tickMs: 15,
+    });
+    const repo = path.join(tmpDir, "app");
+    fs.mkdirSync(repo);
+    git(repo, ["init"]);
+    project = await services.addProject(store, repo);
+  });
+
+  afterEach(async () => {
+    if (runner) runner.stopAll();
+    await rmTree(tmpDir);
+    if (prevSimulate === undefined) delete process.env.CODER_SIMULATE;
+    else process.env.CODER_SIMULATE = prevSimulate;
+    if (prevAgentCmd === undefined) delete process.env.CODER_AGENT_CMD;
+    else process.env.CODER_AGENT_CMD = prevAgentCmd;
+  });
+
+  /** A claude thread mid-task: one finished turn and a live session. */
+  function threadWithHistory() {
+    const thread = services.createThread(store, {
+      projectId: project.id,
+      title: "Mid-task",
+    });
+    store.setMessages(thread.id, [
+      { id: "u1", role: "user", text: "refactor the parser", createdAt: 1 },
+      { id: "a1", role: "assistant", text: "PARSER HALF DONE", createdAt: 2 },
+    ]);
+    store.updateThread(thread.id, { sessionId: "sess-claude" });
+    store.saveNow();
+    return store.getThread(thread.id);
+  }
+
+  it("manual switch: next run's prompt carries the thread's own tail", async () => {
+    const thread = threadWithHistory();
+    const switched = services.setProvider(store, {
+      threadId: thread.id,
+      provider: "codex",
+    });
+    assert.equal(switched.sessionId, null);
+    assert.equal(store.getThread(thread.id).replayContext, true);
+
+    process.env.CODER_AGENT_CMD = agentCmd(logFile);
+    await runner.startRun({ threadId: thread.id, prompt: "keep going" });
+    await waitFor(() => !runner.isRunning(thread.id));
+
+    const [prompt] = readPrompts(logFile);
+    assert.ok(prompt.startsWith("[Hand-off context:"), prompt.slice(0, 80));
+    assert.ok(prompt.includes("PARSER HALF DONE"));
+    assert.ok(prompt.includes("[End context]\n\nkeep going"));
+    // One-shot: cleared once the run starts.
+    assert.ok(!store.getThread(thread.id).replayContext);
+    const users = store.getMessages(thread.id).filter((m) => m.role === "user");
+    assert.equal(users[users.length - 1].text, "keep going");
+  });
+
+  it("quota failover: the resumed run on the new provider carries the tail", async () => {
+    const thread = threadWithHistory();
+    services.setSettings(store, { quotaFailover: ["grok"] });
+    process.env.CODER_AGENT_CMD = agentCmd(
+      logFile,
+      "account quota or balance is exhausted. Please top up.",
+    );
+    await runner.startRun({ threadId: thread.id, prompt: "keep going" });
+    await waitFor(
+      () =>
+        fs.existsSync(logFile) &&
+        readPrompts(logFile).length >= 2 &&
+        !runner.isRunning(thread.id),
+    );
+
+    const [before, after] = readPrompts(logFile);
+    // The original session was live, so the first attempt needed no prefix.
+    assert.ok(before.startsWith("keep going"), before.slice(0, 80));
+    assert.equal(store.getThread(thread.id).provider, "grok");
+    assert.ok(after.startsWith("[Hand-off context:"), after.slice(0, 80));
+    assert.ok(after.includes("PARSER HALF DONE"));
+    assert.ok(after.includes("[End context]\n\nkeep going"));
+    assert.ok(!store.getThread(thread.id).replayContext);
+  });
+
+  it("brand-new thread: switch sets no replay and the run has no prefix", async () => {
+    const thread = services.createThread(store, {
+      projectId: project.id,
+      title: "Fresh",
+    });
+    services.setProvider(store, { threadId: thread.id, provider: "codex" });
+    assert.ok(!store.getThread(thread.id).replayContext);
+
+    process.env.CODER_AGENT_CMD = agentCmd(logFile);
+    await runner.startRun({ threadId: thread.id, prompt: "hello" });
+    await waitFor(() => !runner.isRunning(thread.id));
+    const prompts = readPrompts(logFile);
+    assert.equal(prompts.length, 1);
+    assert.ok(prompts[0].startsWith("hello"), prompts[0].slice(0, 80));
+  });
+
+  it("model switch on a session-pinning provider replays too", () => {
+    const codex = getProvider("codex");
+    const prev = codex.sessionPinsModel;
+    codex.sessionPinsModel = true;
+    try {
+      const thread = threadWithHistory();
+      services.setProvider(store, { threadId: thread.id, provider: "codex" });
+      store.updateThread(thread.id, {
+        sessionId: "sess-codex",
+        replayContext: false,
+      });
+      const other = codex.models.find(
+        (m) => (typeof m === "string" ? m : m.id) !== store.getThread(thread.id).model,
+      );
+      services.setProvider(store, {
+        threadId: thread.id,
+        model: typeof other === "string" ? other : other.id,
+      });
+      const t = store.getThread(thread.id);
+      assert.equal(t.sessionId, null);
+      assert.equal(t.replayContext, true);
+      assert.match(
+        services.buildHandoffPrefix(t, (id) => store.getMessages(id)),
+        /PARSER HALF DONE/,
+      );
+    } finally {
+      codex.sessionPinsModel = prev;
+    }
+  });
+
+  it("moving a session-bearing thread to a new worktree replays too", () => {
+    const thread = threadWithHistory();
+    store.updateThread(thread.id, { worktreePath: path.join(tmpDir, "wt") });
+    const t = store.getThread(thread.id);
+    assert.equal(t.sessionId, null);
+    assert.equal(t.replayContext, true);
+  });
+});