P20.c DiffT
Before 5211acfe95a0c6d82a60e2524b5e46b47fe67a3e
After bb35b941115a0a9f818e8512eebe67c29ee68355
Threshold: ZERO semantic mismatches to declared oracle; ZERO reducer mismatches; all mandatory head assertions PASS. Compare each stream and service/upstream channel independently; ignore only cross-channel arrival interleaving.

NOT_COMPARABLE_TO_BASE: GitWorkflowService.currentBranch is a new method absent from the base. Real Git plus explicitly labelled command/registry adapters exercise the head method.
Declared oracle: Unexpected exit constructs GitCommandError with operation=GitWorkflowService.currentBranch, command=git symbolic-ref, argumentCount3 and lengths; null exit omits exitCode. Spawn failure propagates typed command failure; detect failure maps GitManagerError. No false null success.
HEAD OBSERVATIONS (no fabricated base):
{
  "services": {
    "P20": {
      "assertions": [
        {
          "actual": {
            "exitCode": 128,
            "tag": "GitCommandError"
          },
          "outcome": "PASS",
          "test": "real symbolic-ref unexpected exit is GitCommandError",
          "variant": "unexpected-real-exit-128"
        },
        {
          "actual": "GitCommandError",
          "outcome": "PASS",
          "test": "process adapter error propagates",
          "variant": "process-spawn-failure"
        },
        {
          "actual": {
            "_tag": "GitCommandError",
            "argumentCount": 3,
            "command": "git symbolic-ref",
            "cwd": "<RUN>/repo",
            "detail": "Failed to read the checked-out branch.",
            "operation": "GitWorkflowService.currentBranch",
            "stderrLength": 14,
            "stdoutLength": 14
          },
          "outcome": "PASS",
          "test": "null-exit-error-without-exitCode",
          "variant": "controlled-null-exit"
        },
        {
          "actual": {
            "_tag": "GitManagerError",
            "cause": {},
            "cwd": "<RUN>/repo",
            "detail": "Failed to detect a VCS repository for this Git workflow.",
            "operation": "GitWorkflowService.currentBranch"
          },
          "outcome": "PASS",
          "test": "detect-failure-maps-to-GitManagerError",
          "variant": "controlled-registry-detection-failure"
        }
      ],
      "branchProbeChannel": [],
      "checkpoints": [],
      "clockAdvances": [],
      "finalResultsAndObservations": [
        {
          "argumentCount": 3,
          "command": "git symbolic-ref",
          "detail": "Failed to read the checked-out branch.",
          "exitCode": 128,
          "kind": "typed-error",
          "operation": "GitWorkflowService.currentBranch",
          "stderrLength": 69,
          "stdoutLength": 0,
          "tag": "GitCommandError",
          "variant": "unexpected-real-exit-128"
        },
        {
          "detail": "Controlled missing executable fixture",
          "kind": "typed-error",
          "operation": "GitWorkflowService.currentBranch",
          "tag": "GitCommandError",
          "variant": "process-spawn-failure"
        },
        {
          "argumentCount": 3,
          "command": "git symbolic-ref",
          "kind": "typed-error",
          "operation": "GitWorkflowService.currentBranch",
          "stderrLength": 14,
          "stdoutLength": 14,
          "tag": "GitCommandError",
          "variant": "controlled-null-exit"
        },
        {
          "detail": "Failed to detect a VCS repository for this Git workflow.",
          "kind": "typed-error",
          "operation": "GitWorkflowService.currentBranch",
          "tag": "GitManagerError",
          "variant": "controlled-registry-detection-failure"
        }
      ],
      "invalidationChannel": [],
      "localReadChannel": [],
      "mutations": [
        {
          "action": "corrupt HEAD after successful real Git repository detection to force unexpected symbolic-ref exit",
          "variant": "unexpected-real-exit-128"
        }
      ],
      "pullChannel": [],
      "reconnects": [],
      "rpcStarts": [],
      "upstreamChannel": []
    }
  },
  "streams": {}
}