chore: import upstream snapshot with attribution

test/opencode-auto-context.test.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "node:fs";
+
+// OpenCode plugin needs zero-config memory injection. Plugin
+// already wires experimental.chat.system.transform; this PR threads
+// the /session/start context through a cache so injection happens
+// without a second /context fetch and is documented as the
+// SessionStart-equivalent behaviour.
+describe("OpenCode plugin auto-context injection (#431)", () => {
+  const plugin = readFileSync(
+    "plugin/opencode/agentmemory-capture.ts",
+    "utf-8",
+  );
+
+  it("captures context returned by POST /session/start", () => {
+    expect(plugin).toMatch(/startContextCache\s*=\s*new Map<string,\s*string>/);
+    expect(plugin).toMatch(
+      /postJson\(["']\/session\/start["']/,
+    );
+    // Snapshot `activeSessionId` into a local before the await so the cached
+    // context binds to the session that opened it, not a later one.
+    expect(plugin).toMatch(
+      /const\s+sessionId\s*=\s*activeSessionId[\s\S]*?startContextCache\.set\(sessionId/,
+    );
+  });
+
+  it("chat.system.transform reads cached context first, falls back to /context", () => {
+    expect(plugin).toMatch(/startContextCache\.get\(sid\)/);
+    expect(plugin).toMatch(/postJson\(["']\/context["']/);
+    expect(plugin).toMatch(/startContextCache\.delete\(sid\)/);
+  });
+
+  it("session.deleted clears the cache to avoid stale entries", () => {
+    const deletedBlock = plugin.slice(plugin.indexOf("session.deleted"));
+    expect(deletedBlock).toMatch(/startContextCache\.delete\(sid\)/);
+  });
+});