diff --git a/runner/harness/results.py b/runner/harness/results.py
index 308f61d..b873fac 100644
--- a/runner/harness/results.py
+++ b/runner/harness/results.py
@@ -27,6 +27,7 @@ from __future__ import annotations
 
 import json
 import os
+import shutil
 import xml.etree.ElementTree as ET
 
 from . import level as level_mod
@@ -35,6 +36,17 @@ from . import level as level_mod
 # The dashboard serves these read-only at /runs/<run_id>/... (U0.4). Overridable for tests.
 RUNS_DIR_DEFAULT = "/var/lib/cc-ci-runs"
 
+# The artifact files/dirs a run OWNS in its run dir (written fresh every run).
+_OWNED_ARTIFACTS = (
+    "results.json",
+    "summary.html",
+    "summary.png",
+    "badge.svg",
+    "lint.txt",
+    "screenshot.png",
+    "junit",
+)
+
 
 def runs_dir() -> str:
     return os.environ.get("CCCI_RUNS_DIR", RUNS_DIR_DEFAULT)
@@ -49,6 +61,31 @@ def run_id() -> str:
     return os.environ.get("CCCI_APP_DOMAIN") or os.environ.get("CCCI_RUN_ID") or "manual"
 
 
+def fresh_artifact_dir(path: str) -> str:
+    """Ensure the run artifact dir holds no stale artifacts from a PREVIOUS run with the same id.
+
+    Drone build numbers restarted when its DB was re-created (2026-09-27) while /var/lib/cc-ci-runs
+    still holds old-era dirs numbered into the thousands — a new build reusing an old number would
+    otherwise mix old artifacts into the new run's card (observed 2026-10-05: !testme gitea build 35
+    collided with a May-31 run 35 and embedded custom-html-tiny's fossil screenshot.png, because
+    screenshot.capture() skips its snap when out_path already exists). Removes ONLY the files/dirs
+    this run owns (see _OWNED_ARTIFACTS); anything else in the dir is left untouched. Best-effort
+    (R7): never raises into the run."""
+    os.makedirs(path, exist_ok=True)
+    for name in _OWNED_ARTIFACTS:
+        p = os.path.join(path, name)
+        if os.path.isdir(p):
+            shutil.rmtree(p, ignore_errors=True)
+        else:
+            try:
+                os.remove(p)
+            except FileNotFoundError:
+                pass
+            except OSError:
+                pass  # R7: a stuck file must never fail the run — the card is best-effort anyway
+    return path
+
+
 def junit_file(junit_dir: str, tier: str, source: str, path: str) -> str:
     """Deterministic per-(tier,source,file) JUnit XML path under junit_dir."""
     base = os.path.splitext(os.path.basename(path))[0]
diff --git a/runner/harness/screenshot.py b/runner/harness/screenshot.py
index 15c1867..f8a78fb 100644
--- a/runner/harness/screenshot.py
+++ b/runner/harness/screenshot.py
@@ -142,12 +142,13 @@ def capture(domain: str, out_path: str, *, recipe_meta: dict | None = None) -> s
                 page = context.new_page()
                 if hook is not None:
                     # Recipe-specific safe view (post-login etc.). The hook owns navigation +
-                    # the no-secret-page guarantee; it should call page.screenshot itself, but if
-                    # it doesn't, we still snap the resulting page below. SCREENSHOT(page, ctx) —
-                    # the uniform ctx convention (rcust P3).
+                    # the no-secret-page guarantee; we ALWAYS snap the page after it returns.
+                    # Never trust a pre-existing out_path: a recycled run artifact dir (drone
+                    # build numbers restarted 2026-09-27 while old-era dirs linger) must not get
+                    # its fossil screenshot embedded (observed 2026-10-05, !testme gitea #10
+                    # build 35). SCREENSHOT(page, ctx) — the uniform ctx convention (rcust P3).
                     hook(page, meta_mod.hook_ctx(domain, recipe_meta))
-                    if not os.path.exists(out_path):
-                        _snap_with_blank_retry(page, out_path)
+                    _snap_with_blank_retry(page, out_path)
                 else:
                     # Default: landing page. Accept any rendered status (200 or an auth redirect to a
                     # login form) — both are credential-free and representative of "the app is up".
diff --git a/runner/run_recipe_ci.py b/runner/run_recipe_ci.py
index 19d8167..a2173e1 100644
--- a/runner/run_recipe_ci.py
+++ b/runner/run_recipe_ci.py
@@ -1184,6 +1184,10 @@ def main() -> int:
     # {tier,source,file,rc,junit} record; after the run we assemble results.json (per-stage/per-test +
     # level) into the artifact dir. Best-effort — never changes the verdict (R7).
     run_artifact_dir = os.path.join(results_mod.runs_dir(), results_mod.run_id())
+    # Collision guard (2026-10-05): drone build numbers restarted when its DB was re-created while
+    # old-era run dirs (same numbers, other recipes' artifacts — e.g. a fossil screenshot.png) are
+    # still on disk. Wipe the files THIS run owns so nothing stale survives into the card.
+    results_mod.fresh_artifact_dir(run_artifact_dir)
     junit_dir = os.path.join(run_artifact_dir, "junit")
     records: list[dict] = []
 
diff --git a/tests/unit/test_results.py b/tests/unit/test_results.py
index 7fb0ae1..66cd4ef 100644
--- a/tests/unit/test_results.py
+++ b/tests/unit/test_results.py
@@ -489,3 +489,50 @@ def test_write_results_roundtrip(tmp_path):
     assert path.endswith("/42/results.json")
     with open(path) as f:
         assert json.load(f)["level"] == 3
+
+
+def test_fresh_artifact_dir_removes_owned_stale_artifacts(tmp_path):
+    """Run-dir collision guard (2026-10-05): drone build numbers restarted while old-era run dirs
+    linger in /var/lib/cc-ci-runs — a new build reusing an old number must not mix the old run's
+    artifacts (fossil screenshot.png from ANOTHER recipe) into its card. Only OWNED artifacts go."""
+    d = tmp_path / "35"
+    d.mkdir()
+    (d / "results.json").write_text('{"old": true}')
+    (d / "screenshot.png").write_bytes(b"stale-fossil")
+    (d / "summary.png").write_bytes(b"stale")
+    (d / "badge.svg").write_text("<svg/>")
+    (d / "lint.txt").write_text("old")
+    (d / "summary.html").write_text("<html/>")
+    (d / "junit").mkdir()
+    (d / "junit" / "old.xml").write_text("<x/>")
+    (d / "untracked-thing.bin").write_bytes(b"keep me")  # NOT owned — must survive
+
+    R.fresh_artifact_dir(str(d))
+
+    for name in (
+        "results.json",
+        "screenshot.png",
+        "summary.png",
+        "badge.svg",
+        "lint.txt",
+        "summary.html",
+    ):
+        assert not (d / name).exists(), f"stale owned artifact {name} survived"
+    assert not (d / "junit").exists(), "stale junit dir survived"
+    assert (d / "untracked-thing.bin").read_bytes() == b"keep me", "unowned file was deleted"
+
+
+def test_fresh_artifact_dir_creates_missing_dir(tmp_path):
+    d = tmp_path / "36"
+    out = R.fresh_artifact_dir(str(d))
+    assert out == str(d) and d.is_dir()
+
+
+def test_fresh_artifact_dir_tolerant_of_odd_entries(tmp_path):
+    """R7: never raise into the run — a dir where an owned name is itself a dir must still work."""
+    d = tmp_path / "37"
+    d.mkdir()
+    (d / "screenshot.png").mkdir()  # perverse: a DIRECTORY named screenshot.png
+    (d / "junit").mkdir()
+    R.fresh_artifact_dir(str(d))
+    assert not (d / "screenshot.png").exists() and not (d / "junit").exists()
diff --git a/tests/unit/test_screenshot.py b/tests/unit/test_screenshot.py
index 6c83d90..f9859f1 100644
--- a/tests/unit/test_screenshot.py
+++ b/tests/unit/test_screenshot.py
@@ -184,3 +184,78 @@ def test_screenshot_reachable_through_real_load_path(tmp_path):
     hook = S._load_screenshot_hook(meta)
     assert callable(hook), "SCREENSHOT hook did not survive the orchestrator load path (R2)"
     assert S._load_screenshot_hook(meta_mod.load("no-such", tests_dir=str(tmp_path))) is None
+
+
+# ---- capture() fossil guard (2026-10-05) -----------------------------------------------------
+# Drone build numbers restarted when its DB was re-created while /var/lib/cc-ci-runs still holds
+# old-era dirs numbered into the thousands; run 35 (!testme gitea #10) collided with a May-31 run
+# 35 and embedded custom-html-tiny's fossil screenshot.png because the hook branch SKIPPED the
+# snap when out_path already existed. capture() must always snap fresh.
+
+
+class _FakeLaunchable:
+    def __init__(self, page):
+        self._page = page
+        self.chromium = self
+
+    def launch(self, args=None):
+        return self
+
+    def new_context(self, **kw):
+        return self
+
+    def new_page(self):
+        return self._page
+
+    def close(self):
+        pass
+
+
+class _FakeSyncPlaywright:
+    """sync_playwright() replacement: context-manager factory handing out one fake browser."""
+
+    def __init__(self, page):
+        self._page = page
+
+    def __call__(self):
+        return self
+
+    def __enter__(self):
+        return _FakeLaunchable(self._page)
+
+    def __exit__(self, *exc):
+        return False
+
+
+def _install_fake_playwright(monkeypatch, page):
+    import types
+
+    fake_api = types.ModuleType("playwright.sync_api")
+    fake_api.sync_playwright = _FakeSyncPlaywright(page)
+    fake = types.ModuleType("playwright")
+    fake.sync_api = fake_api
+    monkeypatch.setitem(sys.modules, "playwright", fake)
+    monkeypatch.setitem(sys.modules, "playwright.sync_api", fake_api)
+
+
+def test_capture_overwrites_fossil_screenshot(tmp_path, monkeypatch):
+    """A pre-existing out_path in a recycled run artifact dir must never be embedded: the hook
+    branch snaps fresh regardless (the old exists-guard returned the fossil as 'captured')."""
+    out_path = str(tmp_path / "screenshot.png")
+    with open(out_path, "wb") as f:
+        f.write(b"STALE-FOSSIL-FROM-ANOTHER-RECIPE" * 400)
+
+    fired = {}
+    page = _FakePage([35707])  # one real-sized frame, like a painted page
+
+    def hook(p, ctx):
+        fired["yes"] = True  # navigation only — hooks never save the PNG themselves
+
+    _install_fake_playwright(monkeypatch, page)
+    got = S.capture("gitea.example.org", out_path, recipe_meta={"SCREENSHOT": hook})
+
+    assert got == out_path, "capture must report success after snapping fresh"
+    assert fired.get("yes"), "SCREENSHOT hook must run"
+    assert page.shots == 1, "capture must snap exactly once — the fossil is not a captured frame"
+    with open(out_path, "rb") as f:
+        assert f.read(4) == b"\x89PNG", "out_path still holds the fossil — snap did not overwrite"