Add --record flag to record AI API interactions

[stanislavHamara]

Summary

This PR introduces a --record flag to cagent run, cagent exec, and cagent api commands, enabling users to record AI API interactions to cassette files. These recordings can later be replayed using the existing --fake flag for testing and demo purposes.

Features

• --record flag for exec command: Record a single question/answer interaction

  cagent exec agent.yaml "What's 2+2?" --record=my-recording
  # Creates my-recording.yaml cassette file

• --record flag for run command: Record an interactive TUI session

  cagent run agent.yaml --record
  # Auto-generates cagent-recording-<timestamp>.yaml

• --record flag for api command: Record API server interactions

  cagent api agent.yaml --record=api-recording

• Auto-generated filenames: When --record is used without a value, a timestamped filename is generated automatically

• Mutual exclusivity: --fake and --record flags are mutually exclusive on the api command (you can't replay and record at the same time)

Implementation Details

• Added StartRecordingProxy function in pkg/fake/proxy.go that configures VCR in record mode
• Extracted APIKeyHeaderUpdater to inject real API keys during recording
• Created shared setupRecordingProxy helper in cmd/root/record.go to eliminate duplication
• The recording proxy intercepts requests, forwards them to real AI APIs with proper authentication, and saves responses to cassette files

Testing

Added comprehensive tests:

• Unit tests (pkg/fake/proxy_test.go): APIKeyHeaderUpdater and TargetURLForHost functions
• Unit tests (cmd/root/record_test.go): setupRecordingProxy helper function
• E2E tests (e2e/cagent_record_test.go):
  • TestExec_Record_CreatesCassette - Verifies cassette creation with explicit path
  • TestExec_Record_AutoGeneratesFilename - Verifies auto-generated filenames
  • TestAPI_FakeAndRecord_MutuallyExclusive - Verifies flag mutual exclusivity

Files Changed

File	Change
cmd/root/run.go	Added --record flag and integration
cmd/root/exec.go	Added --record flag
cmd/root/api.go	Added --record flag with --fake mutual exclusivity
cmd/root/record.go	New shared helper for recording proxy setup
cmd/root/record_test.go	Unit tests for record helper
pkg/fake/proxy.go	Added StartRecordingProxy and APIKeyHeaderUpdater
pkg/fake/proxy_test.go	Unit tests for proxy functions
e2e/cagent_record_test.go	E2E tests for --record flag
e2e/proxy_test.go	Refactored to use shared APIKeyHeaderUpdater