diff --git a/src/openultrasast/cli.py b/src/openultrasast/cli.py
index 87dd90c..36608e6 100644
--- a/src/openultrasast/cli.py
+++ b/src/openultrasast/cli.py
@@ -54,6 +54,7 @@ from .pairs import (
 )
 from .policy import assert_rules_resolve, load_policy
 from .preprocess import preprocess_repository, write_preprocess_artifact
+from .provenance import fingerprint
 from .provider.openrouter import OpenRouterEmbeddingClient, OpenRouterError
 from .rank import rank_targets, write_rankings
 from .regress import TRIGGERABLE, CandidateVerdict, run_regression, write_verdicts
@@ -223,6 +224,7 @@ def _run_scan(path: Path, config_path: Path, mode: str, fail_on: str) -> ScanOut
     write_entry_points(entry_points, run.root / "mapping" / "entry_points.json")
     targets = attach_reachability_hints(targets, entry_points)
     write_preprocess_artifact(snapshot, targets, run.root / "preprocess" / "file_targets.json")
+    provenance = runtime.run_stage("provenance", lambda: fingerprint(run.target))
     rankings = runtime.run_stage("rank", lambda: rank_targets(targets))
     prior_learnings = load_false_positive_learnings(ledger_path)
     rankings, calibrations = runtime.run_stage("calibrate", lambda: calibrate_rankings(rankings, prior_learnings))
@@ -520,6 +522,7 @@ def _run_scan(path: Path, config_path: Path, mode: str, fail_on: str) -> ScanOut
             stages=stages_payload(plan),
             complexity=complexity_payload,
             worth_fixing=worth_fixing_payload,
+            provenance=provenance.to_dict(),
         ),
     )
     runtime.finish(status="succeeded")
diff --git a/src/openultrasast/provenance.py b/src/openultrasast/provenance.py
new file mode 100644
index 0000000..7555711
--- /dev/null
+++ b/src/openultrasast/provenance.py
@@ -0,0 +1,117 @@
+"""Deterministic provenance fingerprint: does this tree look agent-authored?
+
+pair-corpus-honesty Requirement 6. Signals are files and directories that agent
+tooling leaves behind, generation markers in text, and git co-author trailers
+over a bounded commit sample. No model is consulted. ``synthetic`` is never
+produced by a scan; it is a catalog declaration only.
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+from dataclasses import dataclass
+from pathlib import Path
+
+PROVENANCE_VALUES = ("human", "agent", "mixed", "synthetic")
+AGENT_SHARE_THRESHOLD = 0.85  # VibeApps method: >=85% of sampled commits carry an agent signal
+DEFAULT_SAMPLE_COMMITS = 200
+
+_AGENT_PATHS = (
+    ".claude",
+    "CLAUDE.md",
+    "AGENTS.md",
+    ".cursor",
+    ".cursorrules",
+    ".windsurf",
+    ".windsurfrules",
+    ".github/copilot-instructions.md",
+    ".codex",
+    ".jules",
+    ".kiro",
+    ".opencode",
+)
+_MARKERS = (
+    ("Generated with Claude Code", "marker:claude-code"),
+    ('<meta name="author" content="Lovable"', "marker:lovable"),
+    ("lovable.dev", "marker:lovable"),
+    ("bolt.new", "marker:bolt"),
+    ("Made with Cursor", "marker:cursor"),
+)
+_TRAILER_RE = re.compile(
+    r"^(?:co-authored-by|generated-by|signed-off-by):\s*.*?(claude|codex|copilot|cursor|devin|jules|gemini|windsurf|aider|openai)\b",
+    re.IGNORECASE | re.MULTILINE,
+)
+_GENERATED_RE = re.compile(r"generated with (claude code|codex|cursor|copilot|devin|jules)", re.IGNORECASE)
+_MARKER_FILES = ("index.html", "README.md", "readme.md", "package.json")
+
+
+@dataclass(frozen=True)
+class Provenance:
+    value: str
+    signals: tuple[str, ...]
+    sampled_commits: int = 0
+    agent_commits: int = 0
+
+    def to_dict(self) -> dict[str, object]:
+        return {
+            "value": self.value,
+            "signals": list(self.signals),
+            "sampled_commits": self.sampled_commits,
+            "agent_commits": self.agent_commits,
+        }
+
+
+def fingerprint(root: Path, *, git: bool = True, sample_commits: int = DEFAULT_SAMPLE_COMMITS) -> Provenance:
+    """Classify ``root`` from deterministic signals only. Never raises into a scan."""
+    signals: list[str] = []
+    for relative in _AGENT_PATHS:
+        if (root / relative).exists():
+            signals.append(f"path:{relative}")
+    for name in _MARKER_FILES:
+        path = root / name
+        if not path.is_file():
+            continue
+        try:
+            text = path.read_text(errors="ignore")[:200_000]
+        except OSError:
+            continue
+        for needle, label in _MARKERS:
+            if needle in text and label not in signals:
+                signals.append(label)
+    sampled = agent = 0
+    if git:
+        sampled, agent, git_signal = _git_trailers(root, sample_commits)
+        if git_signal:
+            signals.append(git_signal)
+    if sampled and agent / sampled >= AGENT_SHARE_THRESHOLD:
+        value = "agent"
+    elif any(not signal.startswith("git:") for signal in signals) or agent:
+        value = "mixed"
+    else:
+        value = "human"
+    return Provenance(value=value, signals=tuple(signals), sampled_commits=sampled, agent_commits=agent)
+
+
+def _git_trailers(root: Path, sample_commits: int) -> tuple[int, int, str]:
+    """(sampled, agent-signalled, signal-label). Missing git is a signal, not an error."""
+    if sample_commits <= 0:
+        return 0, 0, ""
+    try:
+        completed = subprocess.run(
+            ["git", "-C", str(root), "log", f"-{sample_commits}", "--format=%H%x00%B%x1e"],
+            capture_output=True,
+            text=True,
+            timeout=20,
+            check=False,
+        )
+    except (OSError, subprocess.SubprocessError):
+        return 0, 0, "git:unavailable"
+    if completed.returncode != 0:
+        return 0, 0, "git:unavailable"
+    entries = [entry for entry in completed.stdout.split("\x1e") if entry.strip()]
+    sampled = len(entries)
+    agent = sum(1 for entry in entries if _TRAILER_RE.search(entry) or _GENERATED_RE.search(entry))
+    if not sampled:
+        return 0, 0, "git:no-commits"
+    return sampled, agent, f"git:trailers {agent}/{sampled}"
diff --git a/src/openultrasast/reports.py b/src/openultrasast/reports.py
index f14bdd4..fdea267 100644
--- a/src/openultrasast/reports.py
+++ b/src/openultrasast/reports.py
@@ -173,6 +173,7 @@ def write_manifest(
     stages: dict[str, object] | None = None,
     complexity: dict[str, object] | None = None,
     worth_fixing: dict[str, object] | None = None,
+    provenance: dict[str, object] | None = None,
 ) -> None:
     path.parent.mkdir(parents=True, exist_ok=True)
     verification_by_id = _verification_by_id(verifications)
@@ -207,6 +208,8 @@ def write_manifest(
         payload["complexity"] = complexity
     if worth_fixing is not None:
         payload["worth_fixing"] = worth_fixing
+    if provenance is not None:
+        payload["provenance"] = provenance
     path.write_text(json.dumps(payload, indent=2, sort_keys=True) + "\n")
 
 
diff --git a/tests/test_provenance.py b/tests/test_provenance.py
new file mode 100644
index 0000000..475b65b
--- /dev/null
+++ b/tests/test_provenance.py
@@ -0,0 +1,57 @@
+"""Deterministic provenance fingerprint (pair-corpus-honesty Req 6)."""
+
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+
+from openultrasast.provenance import AGENT_SHARE_THRESHOLD, fingerprint
+
+
+def test_empty_tree_is_human_with_no_signals(tmp_path: Path) -> None:
+    result = fingerprint(tmp_path, git=False)
+    assert result.value == "human"
+    assert result.signals == ()
+
+
+def test_agent_config_file_makes_tree_mixed(tmp_path: Path) -> None:
+    (tmp_path / "AGENTS.md").write_text("# agents\n")
+    (tmp_path / ".claude").mkdir()
+    result = fingerprint(tmp_path, git=False)
+    assert result.value == "mixed"
+    assert "path:AGENTS.md" in result.signals and "path:.claude" in result.signals
+
+
+def test_lovable_marker_in_index_html(tmp_path: Path) -> None:
+    (tmp_path / "index.html").write_text('<html><head><meta name="author" content="Lovable" /></head></html>')
+    result = fingerprint(tmp_path, git=False)
+    assert result.value == "mixed"
+    assert "marker:lovable" in result.signals
+
+
+def test_git_trailer_share_over_threshold_is_agent(tmp_path: Path) -> None:
+    subprocess.run(["git", "init", "-q", str(tmp_path)], check=True)
+    env = {"GIT_AUTHOR_NAME": "t", "GIT_AUTHOR_EMAIL": "t@x", "GIT_COMMITTER_NAME": "t", "GIT_COMMITTER_EMAIL": "t@x"}
+    for index in range(10):
+        (tmp_path / f"f{index}.py").write_text("x = 1\n")
+        subprocess.run(["git", "-C", str(tmp_path), "add", "."], check=True)
+        trailer = "\n\nCo-Authored-By: Claude <noreply@anthropic.com>" if index < 9 else ""
+        subprocess.run(
+            ["git", "-C", str(tmp_path), "commit", "-q", "-m", f"c{index}{trailer}"], check=True, env={**env, "PATH": "/usr/bin:/bin"}
+        )
+    result = fingerprint(tmp_path, git=True)
+    assert result.sampled_commits == 10 and result.agent_commits == 9
+    assert result.agent_commits / result.sampled_commits >= AGENT_SHARE_THRESHOLD
+    assert result.value == "agent"
+    assert any(signal.startswith("git:trailers") for signal in result.signals)
+
+
+def test_git_unavailable_is_a_signal_not_an_error(tmp_path: Path) -> None:
+    result = fingerprint(tmp_path, git=True)  # tmp_path is not a repository
+    assert result.value == "human"
+    assert "git:unavailable" in result.signals
+
+
+def test_scan_never_reports_synthetic(tmp_path: Path) -> None:
+    (tmp_path / "CLAUDE.md").write_text("# claude\n")
+    assert fingerprint(tmp_path, git=False).value != "synthetic"