diff --git a/packages/opencode/test/server/httpapi-error-contracts-source.test.ts b/packages/opencode/test/server/httpapi-error-contracts-source.test.ts
new file mode 100644
index 0000000..83c2522
--- /dev/null
+++ b/packages/opencode/test/server/httpapi-error-contracts-source.test.ts
@@ -0,0 +1,37 @@
+import { readdirSync, readFileSync } from "fs"
+import path from "path"
+import { describe, expect, test } from "bun:test"
+
+/**
+ * Structural regression lock for HttpApi error contracts (PRs #6–#8).
+ * Every HttpApiEndpoint.* block in groups/ should declare an `error:` field.
+ * Heuristic: split on HttpApiEndpoint. and require "error:" before the next endpoint.
+ */
+describe("HttpApi group source error contracts", () => {
+  test("every HttpApiEndpoint in groups/ declares error:", () => {
+    const dir = path.join(import.meta.dir, "../../src/server/routes/instance/httpapi/groups")
+    const files = readdirSync(dir).filter((f) => f.endsWith(".ts") && f !== "metadata.ts" && f !== "query.ts")
+    const missing: string[] = []
+
+    for (const file of files) {
+      const text = readFileSync(path.join(dir, file), "utf8")
+      // Skip pure re-export or empty groups
+      if (!text.includes("HttpApiEndpoint.")) continue
+      const parts = text.split(/HttpApiEndpoint\.(get|post|put|delete|patch)\s*\(/)
+      // parts[0] is preamble; then alternating method, body...
+      for (let i = 1; i < parts.length; i += 2) {
+        const method = parts[i]
+        const body = parts[i + 1] ?? ""
+        // endpoint body ends at next top-level annotateMerge closing roughly — take until "}).annotateMerge" or next 800 chars
+        const chunk = body.slice(0, 1200)
+        if (!/\berror\s*:/.test(chunk)) {
+          const nameMatch = chunk.match(/["'`]([a-zA-Z0-9._/-]+)["'`]/)
+          const name = nameMatch?.[1] ?? `idx${i}`
+          missing.push(`${file}:${method}:${name}`)
+        }
+      }
+    }
+
+    expect(missing).toEqual([])
+  })
+})