feat: add postdownload script support for agent types

[vjripoll]

Summary

Implements post-download hook functionality that executes custom scripts after OCI package extraction. This enables packages to perform installation steps, validations, and system configuration that cannot be handled through simple file extraction.

Changes

Core Implementation:

• Added PostDownloadHook struct with path, args, and env fields in package.rs and rendered.rs
• Added post_download_hook: Option<PostDownloadHook> to Package struct
• Created PostDownloadHookExecutor to handle hook execution with proper error handling and timeouts
• Integrated post-download hook execution into OCIPackageManager.install() workflow

Hook Execution:

• Two-part execution model: path = interpreter/command, args[0] = script path, args[1..] = script arguments
• Environment variable support with template variable rendering
• Fixed 300s timeout for hook execution
• Unix: Auto-chmod scripts to 0755 before execution if needed
• Comprehensive error handling for missing commands, execution failures, and timeouts

Agent Type Structure:

deployment:
  packages:
    infra-agent:
      download:
        oci:
          repository: newrelic/infrastructure-bundle
          version: ${nr-var:version}
      post_download_hook:
        path: "/bin/bash"
        args:
          - "bin/install.sh"
          - "--mode=verify"
        env:
          env_vars: "vars"

• Happy path

Jun 10 17:30:48 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[316521]: {"timestamp":"2026-06-10T17:30:48","level":"DEBUG","message":"Postdownload hook found for package ebpf-agent","span":{"id":"ebpf","name":"start_agent"},"spans":[{"id":"ebpf","name":"start_agent"}]}
Jun 10 17:30:48 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[316521]: {"timestamp":"2026-06-10T17:30:48","level":"DEBUG","message":"Executing postdownload","command":"/bin/bash","script":"postdownload.sh","args":"[]","timeout":"300s","span":{"id":"ebpf","name":"start_agent"},"spans":[{"id":"ebpf","name":"start_agent"}]}
Jun 10 17:30:48 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[316521]: {"timestamp":"2026-06-10T17:30:48","level":"DEBUG","message":"Postdownload completed successfully for package ebpf-agent","span":{"id":"ebpf","name":"start_agent"},"spans":[{"id":"ebpf","name":"start_agent"}]}
Jun 10 17:30:48 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[316521]: {"timestamp":"2026-06-10T17:30:48","level":"DEBUG","message":"agent version successfully checked","span":{"id":"ebpf","name":"version_check"},"spans":[{"id":"ebpf","name":"start_agent"},{"id":"ebpf","name":"version_check"}]}
Jun 10 17:30:48 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[316521]: {"timestamp":"2026-06-10T17:30:48","level":"DEBUG","message":"Agent is healthy","span":{"id":"ebpf","name":"process_event"},"spans":[{"id":"ebpf","name":"process_event"}]}

• Error if command or path to the scripts are not in agent type

Jun 10 18:17:20 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[336765]: {"timestamp":"2026-06-10T18:17:20","level":"WARN","message":"Agent is unhealthy","status":"","last_error":"effective agent cannot be assembled from YAML config: error assembling agents: error parsing oci reference: postdownload args must have at least 2 elements: command and script path","span":{"id":"ebpf","name":"process_event"},"spans":[{"id":"ebpf","name":"process_event"}]}

• Error dependecy not found

Jun 11 10:02:35 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[499201]: {"timestamp":"2026-06-11T10:02:35","level":"WARN","command":"/bin/bash","error":"Postdownload failed with exit code Some(18)\nstderr: [ERROR] Linux headers for kernel 6.14.0-27-generic not found at /lib/modules/6.14.0-27-generic/build. Please install them for the eBPF Agent to work.\n","span":{"id":"ebpf","name":"start_agent"},"spans":[{"id":"ebpf","name":"start_agent"}]}
Jun 11 10:02:35 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[499201]: {"timestamp":"2026-06-11T10:02:35","level":"ERROR","message":"Failed to start supervisor: package installation failed: failure installing package: 'ebpf-agent': error attempting to install OCI artifact: Postdownload script failed: Postdownload script execution failed: Postdownload failed with exit code Some(18)\nstderr: [ERROR] Linux headers for kernel 6.14.0-27-generic not found at /lib/modules/6.14.0-27-generic/build. Please install them for the eBPF Agent to work.\n","span":{"id":"ebpf","name":"start_agent"},"spans":[{"id":"ebpf","name":"start_agent"}]}
Jun 11 10:02:35 ubuntu-gnu-linux-24-04-3 newrelic-agent-control[499201]: {"timestamp":"2026-06-11T10:02:35","level":"WARN","message":"Agent is unhealthy","status":"","last_error":"could not start the supervisor: package installation failed: failure installing package: 'ebpf-agent': error attempting to install OCI artifact: Postdownload script failed: Postdownload script execution failed: Postdownload failed with exit code Some(18)\nstderr: [ERROR] Linux headers for kernel 6.14.0-27-generic not found at /lib/modules/6.14.0-27-generic/build. Please install them for the eBPF Agent to work.\n","span":{"id":"ebpf","name":"process_event"},"spans":[{"id":"ebpf","name":"process_event"}]}

[DavSanchez]

Align documentation with the other PostDownloadHook type:

Suggested change

	/// Arguments where first element is the script path, followed by additional arguments.
	/// Arguments passed to the executable on [`path`].

[DavSanchez]

🚀

[DavSanchez]

Not to fix here, but this could have been a From implementation!