fix: detect musl/glibc at runtime for correct Claude binary download

Previously used cfg!(target_env = "musl") which checks compile-time,
causing musl-compiled sandbox-agent to always download musl binaries
even on glibc systems like Debian/E2B.

Now checks for /lib/ld-musl-*.so.1 at runtime to detect the actual
system libc and download the correct Claude binary variant.

docs/troubleshooting.mdx

@@ -0,0 +1,76 @@
+---
+title: "Troubleshooting"
+description: "Common issues and solutions when running sandbox-agent"
+---
+
+## "Agent Process Exited" immediately after sending a message
+
+This typically means the agent (Claude, Codex) crashed on startup. Common causes:
+
+### 1. Network restrictions
+
+The sandbox cannot reach the AI provider's API (`api.anthropic.com` or `api.openai.com`). Test connectivity with:
+
+```bash
+curl -s -o /dev/null -w '%{http_code}' --connect-timeout 5 https://api.anthropic.com/v1/messages
+```
+
+A `000` or timeout means the network is blocked. See [Daytona Network Restrictions](#daytona-network-restrictions) below.
+
+### 2. Missing API key
+
+Ensure `ANTHROPIC_API_KEY` or `OPENAI_API_KEY` is set in the sandbox environment, not just locally.
+
+### 3. Agent binary not found
+
+Verify the agent is installed:
+
+```bash
+ls -la ~/.local/share/sandbox-agent/bin/
+```
+
+### 4. Binary libc mismatch (musl vs glibc)
+
+Claude Code binaries are available in both musl and glibc variants. If you see errors like:
+
+```
+cannot execute: required file not found
+Error loading shared library libstdc++.so.6: No such file or directory
+```
+
+This means the wrong binary variant was downloaded.
+
+**For sandbox-agent 0.2.0+**: Platform detection is automatic. The correct binary (musl or glibc) is downloaded based on the runtime environment.
+
+**For sandbox-agent 0.1.x**: Use Alpine Linux which has native musl support:
+
+```dockerfile
+FROM alpine:latest
+RUN apk add --no-cache curl ca-certificates libstdc++ libgcc bash
+```
+
+## Daytona Network Restrictions
+
+Daytona sandboxes have tier-based network access:
+
+| Tier | Network Access |
+|------|----------------|
+| Tier 1 & 2 | Restricted. **Cannot be overridden.** AI provider APIs blocked by default. |
+| Tier 3 & 4 | Full internet access. Custom allowlists supported. |
+
+If you're on Tier 1/2 and agents fail immediately, you have two options:
+
+1. **Upgrade to Tier 3+** for full network access
+2. **Contact Daytona support** to whitelist `api.anthropic.com` and `api.openai.com` for your organization
+
+The `networkAllowList` parameter only works on Tier 3+:
+
+```typescript
+await daytona.create({
+  snapshot: "my-snapshot",
+  envVars: { ANTHROPIC_API_KEY: "..." },
+  networkAllowList: "api.anthropic.com,api.openai.com", // Tier 3+ only
+});
+```
+
+See [Daytona Network Limits documentation](https://www.daytona.io/docs/en/network-limits/) for details.