diff --git a/packages/opencode/src/agent/agent.ts b/packages/opencode/src/agent/agent.ts
index e643c0293b7b..504e0c56fc9f 100644
--- a/packages/opencode/src/agent/agent.ts
+++ b/packages/opencode/src/agent/agent.ts
@@ -238,6 +238,15 @@ If the spec is clear enough to decompose:
       "labels": ["module:config", "file:src/config/config.ts"],
       "depends_on": [],
       "priority": 0
+    },
+    {
+      "title": "Write OAuth2 login handler",
+      "description": "Implement the login route using the config schema from the previous task",
+      "acceptance_criteria": "Handler validates token, returns 401 on failure. Tests pass.",
+      "task_type": "implementation",
+      "labels": ["module:auth", "file:src/auth/login.ts"],
+       "depends_on": ["Add OAuth2 config schema"],  // use exact title strings from this batch, never numeric indexes
+       "priority": 1
     }
   ]
 }
@@ -250,7 +259,8 @@ RULES FOR GOOD TASK DECOMPOSITION:
 5. Tasks with no shared module:/file: labels can run in parallel
 6. Do not create tasks for work not explicitly required by the issue
 7. Validate your own output: check that no depends_on creates a cycle before responding
-8. Respond with ONLY the JSON object — no markdown, no explanation, no code blocks`,
+8. Respond with ONLY the JSON object — no markdown, no explanation, no code blocks
+ 9. depends_on values must be the EXACT title string of another task in this batch — never use numbers, indexes, or abbreviations`,
       },
       "developer-pipeline": {
         name: "developer-pipeline",
diff --git a/packages/opencode/src/tasks/composer.ts b/packages/opencode/src/tasks/composer.ts
index f07171ff9121..f69b72882351 100644
--- a/packages/opencode/src/tasks/composer.ts
+++ b/packages/opencode/src/tasks/composer.ts
@@ -12,7 +12,7 @@ const ComposerTasksSchema = z.object({
   acceptance_criteria: z.string().min(1),
   task_type: z.enum(["implementation", "test", "research"]),
   labels: z.array(z.string().max(100)).default([]),
-  depends_on: z.array(z.string().min(1).max(200)).default([]),
+   depends_on: z.array(z.string().min(1).max(200)).default([]),
   priority: z.union([z.literal(0), z.literal(1), z.literal(2), z.literal(3), z.literal(4)]),
 })
 
diff --git a/packages/opencode/test/tasks/composer.test.ts b/packages/opencode/test/tasks/composer.test.ts
index c794d93a8259..27c2608f264a 100644
--- a/packages/opencode/test/tasks/composer.test.ts
+++ b/packages/opencode/test/tasks/composer.test.ts
@@ -852,4 +852,56 @@ test("runComposer rolls back tasks on partial creation failure", async () => {
   }
 
   Store.createTask = originalCreate
+})
+
+test("runComposer rejects numeric depends_on values", async () => {
+  const mockSpawn = async () =>
+    JSON.stringify({
+      status: "ready",
+      tasks: [
+        {
+          title: "Task A",
+          description: "desc",
+          acceptance_criteria: "criteria",
+          task_type: "implementation" as const,
+          labels: ["module:test"],
+          depends_on: [],
+          priority: 0,
+        },
+        {
+          title: "Task B",
+          description: "desc",
+          acceptance_criteria: "criteria",
+          task_type: "implementation" as const,
+          labels: ["module:test"],
+          depends_on: [1],  // numeric — should be rejected
+          priority: 1,
+        },
+      ],
+    })
+
+  let threw = false
+  try {
+    await runComposer(
+      {
+        jobId: "job-1",
+        projectId: "test-project",
+        pmSessionId: "session-1",
+        issueNumber: 123,
+        issueTitle: "Add feature",
+        issueBody: "Please add a feature.",
+      },
+      mockSpawn,
+    )
+  } catch (e) {
+    threw = true
+    const msg = (e as Error).message
+    if (!msg.includes("validation failed")) {
+      throw new Error(`Expected validation error for numeric depends_on, got: ${msg}`)
+    }
+  }
+
+  if (!threw) {
+    throw new Error("Expected runComposer to throw validation error for numeric depends_on")
+  }
 })
\ No newline at end of file