diff --git a/src/hooks/atlas/session-last-agent.json.test.ts b/src/hooks/atlas/session-last-agent.json.test.ts
new file mode 100644
index 000000000..196078a50
--- /dev/null
+++ b/src/hooks/atlas/session-last-agent.json.test.ts
@@ -0,0 +1,67 @@
+declare const require: (name: string) => any
+const { afterEach, describe, expect, mock, test, afterAll } = require("bun:test")
+import { mkdtempSync, mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+
+const testDirs: string[] = []
+const TEST_STORAGE_ROOT = join(tmpdir(), `atlas-session-last-agent-${Date.now()}`)
+const TEST_MESSAGE_STORAGE = join(TEST_STORAGE_ROOT, "message")
+
+mock.module("../../shared/opencode-storage-detection", () => ({
+  isSqliteBackend: () => false,
+}))
+
+mock.module("../../shared/opencode-message-dir", () => ({
+  getMessageDir: (sessionID: string) => {
+    const directPath = join(TEST_MESSAGE_STORAGE, sessionID)
+    return require("node:fs").existsSync(directPath) ? directPath : null
+  },
+}))
+
+afterAll(() => { mock.restore() })
+
+afterEach(() => {
+  while (testDirs.length > 0) {
+    const directory = testDirs.pop()
+    if (directory) {
+      rmSync(directory, { recursive: true, force: true })
+    }
+  }
+})
+
+function createTempMessageDir(sessionID: string): string {
+  const directory = mkdtempSync(join(tmpdir(), "atlas-session-last-agent-json-"))
+  testDirs.push(directory)
+  const messageDir = join(TEST_MESSAGE_STORAGE, sessionID)
+  mkdirSync(messageDir, { recursive: true })
+  return messageDir
+}
+
+describe("getLastAgentFromSession JSON backend", () => {
+  test("returns the newest non-compaction agent by message timestamp rather than filename order", async () => {
+    // given
+    const sessionID = "ses_json_last_agent"
+    const messageDir = createTempMessageDir(sessionID)
+    writeFileSync(join(messageDir, "msg_ffff0000_000001.json"), JSON.stringify({
+      agent: "compaction",
+      time: { created: 200 },
+    }), "utf-8")
+    writeFileSync(join(messageDir, "msg_00000000_000999.json"), JSON.stringify({
+      agent: "atlas",
+      time: { created: 100 },
+    }), "utf-8")
+    writeFileSync(join(messageDir, "msg_11111111_000002.json"), JSON.stringify({
+      agent: "sisyphus-junior",
+      time: { created: 50 },
+    }), "utf-8")
+
+    const { getLastAgentFromSession } = await import("./session-last-agent")
+
+    // when
+    const result = await getLastAgentFromSession(sessionID)
+
+    // then
+    expect(result).toBe("atlas")
+  })
+})
diff --git a/src/hooks/atlas/session-last-agent.sqlite.test.ts b/src/hooks/atlas/session-last-agent.sqlite.test.ts
index 9b2a0eb62..a5ce6dbcb 100644
--- a/src/hooks/atlas/session-last-agent.sqlite.test.ts
+++ b/src/hooks/atlas/session-last-agent.sqlite.test.ts
@@ -1,56 +1,71 @@
+export {}
 const { describe, expect, mock, test, afterAll } = require("bun:test")
 
+mock.module("../../shared/opencode-storage-detection", () => ({
+  isSqliteBackend: () => true,
+}))
+
 afterAll(() => { mock.restore() })
 
-async function importFreshSessionLastAgentModule() {
-  mock.module("../../shared/opencode-message-dir", () => ({
-    getMessageDir: () => null,
-  }))
+const { getLastAgentFromSession } = await import("./session-last-agent")
 
-  mock.module("../../shared/opencode-storage-detection", () => ({
-    isSqliteBackend: () => true,
-  }))
-
-  const module = await import(`./session-last-agent?test=${Date.now()}-${Math.random()}`)
-  mock.restore()
-  return module
-}
-
-const { getLastAgentFromSession } = await importFreshSessionLastAgentModule()
-
-function createMockClient(messages: Array<{ info?: { agent?: string } }>) {
-  return {
-    session: {
-      messages: async () => ({ data: messages }),
-    },
-  }
-}
-
-describe("getLastAgentFromSession sqlite branch", () => {
-  test("should skip compaction and return the previous real agent from sqlite messages", async () => {
+describe("getLastAgentFromSession SQLite backend ordering", () => {
+  test("returns newest non-compaction agent using time.created and id tie-breaker", async () => {
     // given
-    const client = createMockClient([
-      { info: { agent: "atlas" } },
-      { info: { agent: "compaction" } },
-    ])
+    const client = {
+      session: {
+        messages: async () => ({
+          data: [
+            { id: "msg_0001", info: { agent: "atlas", time: { created: 100 } } },
+            { id: "msg_0003", info: { agent: "compaction", time: { created: 200 } } },
+            { id: "msg_0002", info: { agent: "sisyphus-junior", time: { created: 100 } } },
+          ],
+        }),
+      },
+    }
 
     // when
-    const result = await getLastAgentFromSession("ses_sqlite_compaction", client)
+    const result = await getLastAgentFromSession("ses_sqlite_last_agent", client as never)
 
     // then
-    expect(result).toBe("atlas")
+    expect(result).toBe("sisyphus-junior")
   })
 
-  test("should return null when sqlite history contains only compaction", async () => {
+  test("handles equal timestamps with random-looking ids deterministically", async () => {
     // given
-    const client = createMockClient([{ info: { agent: "compaction" } }])
+    const client = {
+      session: {
+        messages: async () => ({
+          data: [
+            { id: "msg_a91f00ab", info: { agent: "atlas", time: { created: 100 } } },
+            { id: "msg_f0e1d2c3", info: { agent: "compaction", time: { created: 200 } } },
+            { id: "msg_d4c3b2a1", info: { agent: "sisyphus-junior", time: { created: 100 } } },
+          ],
+        }),
+      },
+    }
 
     // when
-    const result = await getLastAgentFromSession("ses_sqlite_only_compaction", client)
+    const result = await getLastAgentFromSession("ses_sqlite_last_agent_equal_time", client as never)
+
+    // then
+    expect(result).toBe("sisyphus-junior")
+  })
+
+  test("returns null instead of throwing when SQLite message lookup fails", async () => {
+    // given
+    const client = {
+      session: {
+        messages: async () => {
+          throw new Error("sqlite lookup failed")
+        },
+      },
+    }
+
+    // when
+    const result = await getLastAgentFromSession("ses_sqlite_error", client as never)
 
     // then
     expect(result).toBeNull()
   })
 })
-
-export {}
diff --git a/src/hooks/atlas/session-last-agent.ts b/src/hooks/atlas/session-last-agent.ts
index 6c6b821db..43933b33f 100644
--- a/src/hooks/atlas/session-last-agent.ts
+++ b/src/hooks/atlas/session-last-agent.ts
@@ -15,20 +15,27 @@ function isCompactionAgent(agent: unknown): boolean {
 
 function getLastAgentFromMessageDir(messageDir: string): string | null {
   try {
-    const files = readdirSync(messageDir)
+    const messages = readdirSync(messageDir)
       .filter((fileName) => fileName.endsWith(".json"))
-      .sort()
-
-    for (let i = files.length - 1; i >= 0; i--) {
-      const fileName = files[i]
-      try {
-        const content = readFileSync(join(messageDir, fileName), "utf-8")
-        const parsed = JSON.parse(content) as { agent?: unknown }
-        if (typeof parsed.agent === "string" && !isCompactionAgent(parsed.agent)) {
-          return parsed.agent.toLowerCase()
+      .map((fileName) => {
+        try {
+          const content = readFileSync(join(messageDir, fileName), "utf-8")
+          const parsed = JSON.parse(content) as { agent?: unknown; time?: { created?: unknown } }
+          return {
+            fileName,
+            agent: parsed.agent,
+            createdAt: typeof parsed.time?.created === "number" ? parsed.time.created : Number.NEGATIVE_INFINITY,
+          }
+        } catch {
+          return null
         }
-      } catch {
-        continue
+      })
+      .filter((message): message is { fileName: string; agent: unknown; createdAt: number } => message !== null)
+      .sort((left, right) => right.createdAt - left.createdAt || right.fileName.localeCompare(left.fileName))
+
+    for (const message of messages) {
+      if (typeof message.agent === "string" && !isCompactionAgent(message.agent)) {
+        return message.agent.toLowerCase()
       }
     }
   } catch {
@@ -43,16 +50,30 @@ export async function getLastAgentFromSession(
   client?: SessionMessagesClient
 ): Promise<string | null> {
   if (isSqliteBackend() && client) {
-    const response = await client.session.messages({ path: { id: sessionID } })
-    const messages = normalizeSDKResponse(response, [] as Array<{ info?: { agent?: string } }>, {
-      preferResponseOnMissingData: true,
-    })
+    try {
+      const response = await client.session.messages({ path: { id: sessionID } })
+      const messages = normalizeSDKResponse(response, [] as Array<{ id?: string; info?: { agent?: string; time?: { created?: number } } }>, {
+        preferResponseOnMissingData: true,
+      }).sort((left, right) => {
+        const leftTime = (left as { info?: { time?: { created?: number } } }).info?.time?.created ?? Number.NEGATIVE_INFINITY
+        const rightTime = (right as { info?: { time?: { created?: number } } }).info?.time?.created ?? Number.NEGATIVE_INFINITY
+        if (leftTime !== rightTime) {
+          return rightTime - leftTime
+        }
 
-    for (let i = messages.length - 1; i >= 0; i--) {
-      const agent = messages[i].info?.agent
-      if (typeof agent === "string" && !isCompactionAgent(agent)) {
-        return agent.toLowerCase()
+        const leftId = typeof left.id === "string" ? left.id : ""
+        const rightId = typeof right.id === "string" ? right.id : ""
+        return rightId.localeCompare(leftId)
+      })
+
+      for (const message of messages) {
+        const agent = message.info?.agent
+        if (typeof agent === "string" && !isCompactionAgent(agent)) {
+          return agent.toLowerCase()
+        }
       }
+    } catch {
+      return null
     }
 
     return null