diff --git a/src/adapters/opencode.ts b/src/adapters/opencode.ts
index 5806950..3ef4413 100644
--- a/src/adapters/opencode.ts
+++ b/src/adapters/opencode.ts
@@ -1,5 +1,5 @@
 import path from "node:path";
-import { copyFile, readFile } from "node:fs/promises";
+import { copyFile, readdir, readFile } from "node:fs/promises";
 import type {
   ExplainInput,
   ExplainResult,
@@ -160,7 +160,10 @@ export class OpenCodeAdapter extends BaseAdapter implements RunnerAdapter {
       throw new Error(`OpenCode run failed: ${runError}`);
     }
 
-    const sessionId = this.extractSessionId(stdout) ?? this.extractSessionId(stderr);
+    const sessionId =
+      this.extractSessionId(stdout) ??
+      this.extractSessionId(stderr) ??
+      (await this.extractSessionIdFromRuntimeLog(input));
 
     if (sessionId === undefined) {
       throw new Error(
@@ -393,6 +396,33 @@ export class OpenCodeAdapter extends BaseAdapter implements RunnerAdapter {
     const match = text.match(/\b(ses_[A-Za-z0-9]+)\b/);
     return match?.[1];
   }
+
+  private async extractSessionIdFromRuntimeLog(input: RunInput): Promise<string | undefined> {
+    const logDir = path.join(getOpenCodePaths(input).dataHome, "opencode", "log");
+    let entries: string[];
+
+    try {
+      entries = await readdir(logDir);
+    } catch (error) {
+      if (isMissingFileError(error)) {
+        return undefined;
+      }
+      throw error;
+    }
+
+    for (const entry of entries.toSorted().toReversed()) {
+      if (!entry.endsWith(".log")) {
+        continue;
+      }
+
+      const sessionId = this.extractSessionId(await readFile(path.join(logDir, entry), "utf8"));
+      if (sessionId !== undefined) {
+        return sessionId;
+      }
+    }
+
+    return undefined;
+  }
 }
 
 function getOpenCodeRuntimeRoot(input: RunInput): string {
@@ -533,8 +563,12 @@ function parseOpenCodeExport(value: string): OpenCodeExport & { messages: OpenCo
   try {
     parsed = JSON.parse(value);
   } catch (error) {
-    const reason = error instanceof Error ? error.message : String(error);
-    throw new Error(`OpenCode export returned invalid JSON: ${reason}`);
+    try {
+      parsed = JSON.parse(extractJsonObject(value));
+    } catch {
+      const reason = error instanceof Error ? error.message : String(error);
+      throw new Error(`OpenCode export returned invalid JSON: ${reason}`);
+    }
   }
 
   if (!isOpenCodeExport(parsed)) {
@@ -544,6 +578,17 @@ function parseOpenCodeExport(value: string): OpenCodeExport & { messages: OpenCo
   return parsed;
 }
 
+function extractJsonObject(value: string): string {
+  const start = value.indexOf("{");
+  const end = value.lastIndexOf("}");
+
+  if (start === -1 || end === -1 || end < start) {
+    throw new Error("OpenCode export output did not contain a JSON object.");
+  }
+
+  return value.slice(start, end + 1);
+}
+
 function isOpenCodeExport(
   value: unknown,
 ): value is OpenCodeExport & { messages: OpenCodeMessage[] } {
diff --git a/test/adapters/opencode.test.ts b/test/adapters/opencode.test.ts
index fdc8a90..41a6a20 100644
--- a/test/adapters/opencode.test.ts
+++ b/test/adapters/opencode.test.ts
@@ -16,7 +16,7 @@ afterEach(async () => {
 test("OpenCodeAdapter collect parses export payload wrapped in extra text", async () => {
   const tempDir = await createTempDir();
   const adapter = new ExportingOpenCodeAdapter({
-    exportStdout: JSON.stringify({
+    exportStdout: `Exporting session: ses_123\n${JSON.stringify({
       info: { id: "ses_123" },
       messages: [
         {
@@ -36,7 +36,7 @@ test("OpenCodeAdapter collect parses export payload wrapped in extra text", asyn
           ],
         },
       ],
-    }),
+    })}`,
   });
 
   const input = {
@@ -88,6 +88,46 @@ test("OpenCodeAdapter collect parses export payload wrapped in extra text", asyn
   });
 });
 
+test("OpenCodeAdapter collect falls back to runtime log session id", async () => {
+  const tempDir = await createTempDir();
+  const adapter = new ExportingOpenCodeAdapter({
+    exportStdout: JSON.stringify({
+      info: { id: "ses_fromlog" },
+      messages: [],
+    }),
+    expectedSessionId: "ses_fromlog",
+  });
+
+  const input = {
+    ...createRunInput(),
+    cwd: tempDir,
+    artifactsDir: path.join(tempDir, "artifacts"),
+  } satisfies RunInput;
+  const logDir = path.join(input.artifactsDir, "opencode-xdg", "data", "opencode", "log");
+  await mkdir(logDir, { recursive: true });
+  await writeFile(
+    path.join(logDir, "2026-05-15T115637.log"),
+    "INFO service=session id=ses_fromlog created\n",
+    "utf8",
+  );
+
+  const stdoutPath = path.join(tempDir, "stdout.log");
+  const stderrPath = path.join(tempDir, "stderr.log");
+  await writeFile(stdoutPath, "", "utf8");
+  await writeFile(stderrPath, "Database migration complete.\n", "utf8");
+
+  const artifacts = await adapter.collect(
+    {
+      ...createArtifacts(),
+      stdoutPath,
+      stderrPath,
+    },
+    input,
+  );
+
+  expect(artifacts.sessionId).toBe("ses_fromlog");
+});
+
 test("OpenCodeAdapter collect fails when export output is invalid JSON", async () => {
   const tempDir = await createTempDir();
   const adapter = new ExportingOpenCodeAdapter({
@@ -335,7 +375,7 @@ async function createTempDir(): Promise<string> {
 class ExportingOpenCodeAdapter extends OpenCodeAdapter {
   exportEnv?: Record<string, string>;
 
-  constructor(private readonly testOptions: { exportStdout: string }) {
+  constructor(private readonly testOptions: { exportStdout: string; expectedSessionId?: string }) {
     super();
   }
 
@@ -346,7 +386,7 @@ class ExportingOpenCodeAdapter extends OpenCodeAdapter {
     options?: { env?: Record<string, string> },
   ) {
     expect(command).toBe("opencode");
-    expect(args).toEqual(["export", "ses_123"]);
+    expect(args).toEqual(["export", this.testOptions.expectedSessionId ?? "ses_123"]);
     this.exportEnv = options?.env;
 
     const stdoutPath = path.join(input.artifactsDir, "stdout.log");