feat(agent): migrate OpenCode 2 runtime and sandbox tools

Upgrade the runtime and native plugin API to OpenCode 2.0.24. Restore
session-scoped learning, credential renewal, typed project queries and
controlled frontend actions from the legacy Agent.

Replace host Shell execution with an approved Landlock/seccomp executor
and persistent per-session workspaces. Add typed Bocha search and Tianditu
geocoding bridges using the owning session credential. Require a working
kernel sandbox before startup and persist workspace files in deployments.

Validation completed before this commit: TypeScript checks, 150 Bun tests,
Docker build and UID 10001 sandbox execution, native Shell approval and
session recovery. Tianditu succeeded; Bocha currently reports exhausted
account quota. Unrelated investigation-report contract work is excluded.

src/runtime/opencode2-config.ts

@@ -0,0 +1,20 @@
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+
+// A conversation Location can be outside the checkout. Load only the trusted
+// service assets explicitly, rather than relying on its current directory.
+export function serviceOpencodeConfig(input: Record<string, unknown>) {
+  const agents = (input.agents ?? {}) as Record<string, unknown>;
+  const instruction = (agents.instruction ?? {}) as Record<string, unknown>;
+  const system = readFileSync(resolve(".opencode/agents/instruction.md"), "utf8")
+    .replace(/^---\s*\n[\s\S]*?\n---\s*\n/, "");
+  return {
+    ...input,
+    snapshots: false,
+    plugins: ["*", ...((input.plugins ?? []) as unknown[]), resolve(".opencode/tjwater-plugin")],
+    skills: [resolve(process.env.OPENCODE_SKILLS_ROOT_DIR ?? ".opencode/skills")],
+    agents: { ...agents, instruction: {
+      description: "TJWater structured data and UI agent", mode: "primary", ...instruction, system,
+    } },
+  };
+}