Implement RFC #0131 - Build Observability telemetry specification (Buildpack spec)

[Copilot]

Restores OpenTelemetry telemetry support that was reverted from buildpack.md and image_extension.md in commit 17e6edc. These changes belong in the buildpack API spec (buildpack/0.13) rather than the platform spec.

Changes

buildpack.md

• Added CNB_OTEL_TRACEPARENT and CNB_OTEL_LOG_PATH environment variables to detect and build phase inputs
• Documented CNB_OTEL_LOG_PATH as output for both phases
• Added MAY clauses permitting buildpacks to write telemetry in OpenTelemetry File Exporter format

image_extension.md

• Added MAY clause permitting extensions to write telemetry to CNB_OTEL_LOG_PATH

Example

Buildpacks can now optionally emit telemetry during detect or build:

# Platform provides path
CNB_OTEL_LOG_PATH=/layers/tracing/buildpacks/example@1.0.0-detect.jsonl

# Buildpack writes OpenTelemetry JSONL format
echo '{"resourceSpans":[...]}' >> $CNB_OTEL_LOG_PATH

The CNB_OTEL_TRACEPARENT variable enables correlation with platform traces via W3C Trace Context.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/buildpacks/spec/pulls/421/commits
  • Triggering command: /usr/bin/curl curl -s REDACTED (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Pull OTEL changes from buildpack.md and image_extension.md into a new PR</issue_title>
<issue_description>Commit that reverted the changes out: 17e6edc

The OTEL changes introducing CNB_OTEL_LOG_PATH and the behavior documented need to be in a new PR against buildpack/0.13.</issue_description>

<agent_instructions>Bring in the reverted commit changes in a new branch PR</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Pull OTEL changes from buildpack.md and image_extension.md into a new PR #425

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