refactor(lib): remove the dead build-info.json registration read-path

[max-parke-scale]

Removes the never-fed build-info.json → registration_metadata read-path.

Why

• Never fed. No producer has ever written build-info.json. The read path landed 2025-09 (Send build info with registration metadata #103) expecting an external build system that never materialized, so the registration git-provenance fields have been null for ~9 months.
• Redundant. AgentexCloudDeploy.build_id is an FK to AgentexCloudBuild, so a deployment's source provenance derives from the build record (the source_* columns AGX1-418 adds) over that join — no need to denormalize onto registration_metadata.

What

• Remove FastACP.locate_build_info_path() + its call in FastACP.create().
• Remove registration.get_build_info() and the registration_metadata = get_build_info() seed — registration_metadata still carries deployment_id / agent_card.
• Remove the now-unused BUILD_INFO_PATH env-var const/field.
• Update the 3 test_agent_card.py tests that mocked get_build_info.

Full lib suite green (877 passed); ruff/pyright clean. Tracked in AGX1-419; the server-side DeploymentHistory git fields are the other (cross-team, breaking) half tracked there.

🧑‍💻🤖 — posted via Claude Code

Greptile Summary

This PR removes the unused build-info registration metadata path. The main changes are:

• Removed BUILD_INFO_PATH from environment variable parsing.
• Removed FastACP probing for nearby build-info.json files.
• Removed get_build_info() from agent registration.
• Kept registration metadata limited to deployment id and agent card.
• Updated agent card registration tests for the new metadata behavior.

Confidence Score: 5/5

Safe to merge based on the scoped removal of unused build-info metadata plumbing and corresponding test updates.

The changes are narrowly focused on deleting an unfed read path while preserving deployment id and agent card registration metadata, with no issues identified in the changed behavior.

T-Rex Logs

What T-Rex did

• The register_agent path was run with a mocked HTTP post capture to record the before-state metadata, confirming the base keys for the card+deployment+build-info path and that build-info-only shows non-null metadata.
• The register_agent path was run again to capture the after-state metadata, showing head keys limited to agent_card and deployment_id for card+deployment+build-info; deployment-only includes deployment_id; build-info-only/no-metadata yields registration_metadata:null; and both runs exited with code 0.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "refactor(lib): remove the dead build-inf..." | Re-trigger Greptile}