container: Add Pi coding agent (pi.dev) as a third harness

- Install @earendil-works/pi-coding-agent globally via npm in the
  image so it survives the home directory bind mount
- Add pi subcommand forwarding PI_* and provider key prefixes
- Add pi shell wrapper alias
- Build with --network host so image builds work on hosts where the
  Docker bridge network cannot create veth pairs

agent-container.py

@@ -18,6 +18,7 @@ USAGE = """\
 Usage:
   agent-container opencode [args...]   Run OpenCode in the container
   agent-container claude [args...]     Run Claude Code in the container
+  agent-container pi [args...]         Run Pi in the container
   agent-container update               Rebuild image with latest versions
   agent-container purge                Remove all containers, image, and data
 """
@@ -80,6 +81,41 @@ class AgentContainer:
                 env_prefixes=["ANTHROPIC_", "CLAUDE_"],
                 extra_env={"DISABLE_AUTOUPDATER": "1"},
             )
+        elif command == "pi":
+            # Forward pi's own variables plus the API key prefixes of its
+            # supported providers (see pi docs: providers.md). Auth via
+            # /login persists in the shared container home instead.
+            self._run_tool(
+                "pi",
+                args,
+                env_prefixes=[
+                    "PI_",
+                    "ANTHROPIC_",
+                    "ANT_LING_",
+                    "OPENAI_",
+                    "AZURE_",
+                    "GOOGLE_",
+                    "GEMINI_",
+                    "DEEPSEEK_",
+                    "NVIDIA_",
+                    "MISTRAL_",
+                    "GROQ_",
+                    "CEREBRAS_",
+                    "CLOUDFLARE_",
+                    "XAI_",
+                    "OPENROUTER_",
+                    "AI_GATEWAY_",
+                    "ZAI_",
+                    "KIMI_",
+                    "MINIMAX_",
+                    "QWEN_",
+                    "OPENCODE_",
+                    "FIREWORKS_",
+                    "TOGETHER_",
+                    "BASETEN_",
+                    "OLLAMA_",
+                ],
+            )
         elif command == "update":
             self.update()
         elif command == "purge":
@@ -221,6 +257,10 @@ class AgentContainer:
         cmd = [
             "docker",
             "build",
+            # Use host networking during build so the build works on hosts
+            # where the default bridge network cannot create veth pairs
+            "--network",
+            "host",
             "--build-arg",
             f"USERNAME={self.host_username}",
             "--build-arg",