Prevent agent log loss during pier exec

[jbragg]

Summary

Agent session logs were lost when containers stopped because pier exec
didn't capture output or set the env vars agents need to write to the
mounted volume. This PR fixes log capture for all Harbor agents.

• Session recording: agent commands are auto-detected via Harbor's
  agent registry and wrapped with script(1) to record output while
  preserving TTY for interactive use
• Config-dir env vars: CLAUDE_CONFIG_DIR and CODEX_HOME set on
  every container exec so structured session logs land in the mounted
  volume (user -e overrides win)
• Per-session isolation: each pier exec gets a timestamped directory
  under /logs/agent/ so multiple sessions don't overwrite each other
• Post-run artifacts: gemini trajectory copy and hermes session export
  run after the agent exits
• --session flag: pier verify --session <ts> and
  pier capture --session <ts> select a specific session when multiple
  exist
• DEVELOPER.md: architecture docs for log capture, session layout,
  Harbor integration, and tech debt

Builds on #3 — that PR ensures verify/capture work when logs exist;
this PR ensures logs exist.

[Copilot]

Pull request overview

Improves pier exec reliability in container mode by ensuring agent session logs and interactive output are persisted to the host-mounted Harbor agent log volume, enabling pier verify/pier capture to consistently extract trajectories.

Changes:

• Auto-detect Harbor agents on pier exec and record interactive output to per-exec timestamped directories under /logs/agent/ (host: .pier/_harbor/agent/).
• Always set CLAUDE_CONFIG_DIR and CODEX_HOME for container execs (with user -e overrides winning) and run agent-specific post-run artifact collection (gemini/hermes).
• Add --session to pier verify / pier capture to select a specific per-exec session directory when multiple exist; add docs and test coverage.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
README.md	Updates pier exec docs and points dev setup/testing guidance to DEVELOPER.md.
DEVELOPER.md	New developer guide including architecture notes for log capture/session layout.
pier/harbor_bridge.py	Adds log-capture env helpers, agent binary registry mapping, per-session selection helpers, and script(1) wrapping support in exec_in_container().
pier/cli.py	Implements agent auto-detection + per-exec session dirs + --session support for verify/capture and post-run artifact collection.
pier/tests/test_pier_cli.py	Adds CLI unit tests for log-capture env behavior, auto-detect/recording behavior, and --session flag behavior.
pier/tests/test_harbor_bridge.py	Adds unit tests for new harbor_bridge helpers and an end-to-end extraction/assembly pipeline test.
pier/tests/test_docker_integration.py	Adds Docker integration tests verifying log-capture env vars are present and bind-mounted/writable.
pier/tests/test_agent_integration.py	Extends agent integration tests to assert per-session tee output and log env vars.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

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