diff --git a/fixos/cli/_cleanup_space.py b/fixos/cli/_cleanup_space.py
index 3987039..57f1b05 100644
--- a/fixos/cli/_cleanup_space.py
+++ b/fixos/cli/_cleanup_space.py
@@ -1162,7 +1162,7 @@ def _docker_buildx_builders() -> list[dict] | None:
     return builders
 
 
-def _builder_cache_bytes(name: str) -> tuple[int, int] | None:
+def _builder_cache_bytes(name: str) -> tuple[int, int | None] | None:
     """Return (total, reclaimable) bytes of a builder's cache or None."""
     try:
         result = _run_cmd(
@@ -1183,23 +1183,62 @@ def _builder_cache_bytes(name: str) -> tuple[int, int] | None:
             reclaimable = _size_to_bytes(match.group(2))
     if total is None:
         return None
-    return total, reclaimable if reclaimable is not None else total
+    return total, reclaimable
+
+
+def _container_image_ids() -> set[str] | None:
+    """Read image references for running and stopped containers, or unknown."""
+    try:
+        result = _run_cmd(
+            ["docker", "container", "ls", "--all", "--quiet", "--no-trunc"]
+        )
+        if result.returncode != 0:
+            return None
+        containers = result.stdout.split()
+        if not containers:
+            return set()
+        if any(not re.fullmatch(r"[0-9a-f]{64}", item) for item in containers):
+            return None
+        result = _run_cmd(
+            ["docker", "container", "inspect", "--format", "{{.Image}}", *containers]
+        )
+        if result.returncode != 0:
+            return None
+        images = result.stdout.split()
+        if len(images) != len(containers) or any(
+            not re.fullmatch(r"sha256:[0-9a-f]{64}", item) for item in images
+        ):
+            return None
+        return set(images)
+    except (OSError, subprocess.TimeoutExpired):
+        return None
 
 
 def _dangling_images() -> dict | None:
-    """Return count and approx bytes of dangling (<none>) images."""
+    """Count unreferenced dangling images; their logical sizes can share layers."""
     try:
         result = _run_cmd(
-            ["docker", "images", "-f", "dangling=true", "--format", "{{.Size}}"]
+            [
+                "docker", "images", "--no-trunc", "-f", "dangling=true",
+                "--format", "{{.ID}}\t{{.Size}}",
+            ]
         )
     except (OSError, subprocess.TimeoutExpired):
         return None
     if result.returncode != 0:
         return None
+    rows = [line.split("\t") for line in result.stdout.splitlines() if line.strip()]
+    if any(
+        len(row) != 2 or not re.fullmatch(r"sha256:[0-9a-f]{64}", row[0])
+        for row in rows
+    ):
+        return None
+    used = _container_image_ids() if rows else set()
     sizes = [
-        _size_to_bytes(line) for line in result.stdout.splitlines() if line.strip()
+        _size_to_bytes(size) for image, size in rows
+        if used is None or image not in used
     ]
-    return {"count": len(sizes), "bytes": sum(sizes)}
+    return {"count": len(sizes), "bytes": sum(sizes), "usage_known": used is not None}
 
 
 def _docker_buildcache_scan() -> dict:
@@ -1238,7 +1277,10 @@ def _docker_buildcache_scan() -> dict:
                 "driver": "docker",
                 "current": False,
                 "total_bytes": dangling["bytes"],
-                "reclaimable_bytes": dangling["bytes"],
+                # Shared layers and concurrent container creation prevent a
+                # logical image-size sum from predicting actual prune results.
+                "reclaimable_bytes": None,
+                "usage_known": dangling["usage_known"],
                 "count": dangling["count"],
                 "command": ["docker", "image", "prune", "--force"],
             }
@@ -1284,6 +1326,12 @@ def _cleanup_docker_buildcache(
                 if note
                 else f"reclaimable ~{_format_bytes(reclaimable)}"
             )
+        else:
+            note = f"{note}, odzyskiwalny rozmiar nieznany".lstrip(", ")
+        if target["kind"] == "dangling-images":
+            note += "; suma rozmiarów obrazów obejmuje współdzielone warstwy"
+            if not target["usage_known"]:
+                note += "; użycie przez kontenery nieznane"
         candidates.append(
             {
                 "description": label,
diff --git a/project/ticket-113/README.md b/project/ticket-113/README.md
new file mode 100644
index 0000000..7dea03e
--- /dev/null
+++ b/project/ticket-113/README.md
@@ -0,0 +1,34 @@
+# Ticket 113: Report Docker dangling-image reclaimability honestly
+
+- **ID**: ticket-113
+- **Owner**: agent:codex
+- **Status**: IN_PROGRESS
+- **Workflow state**: PUBLICATION
+- **Created**: 2026-10-31
+
+## Goal and scope
+
+On this host FixOS advertised 22.6 GB of dangling images as reclaimable, but
+Docker prune reclaimed 0 B. Three 7 GB images were still referenced by running
+containers. Exclude referenced images from the prune inventory and distinguish
+logical image sizes from unknown shared-layer reclaimability. A missing
+BuildKit reclaimable measurement must remain unknown.
+
+SESSION_EXECUTION_AUTHORIZATION: the user requested continuing FixOS repairs,
+cleanup and protected publication on 2026-10-31. This bounded diagnostic repair
+uses that authority; independent approval and merge remain controller-owned.
+
+## Acceptance criteria
+
+- [x] AC-01: Images referenced by running or stopped containers are excluded;
+  failed usage reads and shared-layer totals never claim known reclaimability.
+- [x] AC-02: Missing BuildKit reclaimable measurements remain unknown; CLI and
+  JSON output distinguish unknown amounts; existing safe prune commands remain.
+- [ ] AC-03: Local checks pass and exact-head independent publication is requested.
+
+## Validation
+
+- Nine regression cases failed before the fix; all 10 now pass.
+- Focused cleanup suites: 32 passed. Ruff, import sorting and managed governance passed.
+- Live read-only inventory no longer lists images used by containers as prune candidates.
+- Full governed checks and exact-head independent publication run through Goal and the protected Validator.
diff --git a/project/ticket-113/intent.json b/project/ticket-113/intent.json
new file mode 100644
index 0000000..516ffd6
--- /dev/null
+++ b/project/ticket-113/intent.json
@@ -0,0 +1,79 @@
+{
+  "schema": "new-project.intent/v3",
+  "ticket": "ticket-113",
+  "summary": "Report Docker dangling-image reclaimability honestly",
+  "workstream": "application",
+  "classification": {
+    "kind": "BUG",
+    "priority": "P2",
+    "origin": "requested"
+  },
+  "allowedPaths": [
+    "project/ticket-113/**",
+    "fixos/cli/_cleanup_space.py",
+    "tests/unit/test_cleanup_docker_buildcache.py"
+  ],
+  "forbiddenPaths": [
+    "project/ticket-*/user-*.md"
+  ],
+  "stacks": [
+    "python"
+  ],
+  "dependsOn": [],
+  "conflictsWith": [],
+  "integrationTicket": null,
+  "delivery": {
+    "acceptedBaseSha": "0afa281482622cf1816293e5a5e9e61b5d043e46",
+    "targetBranch": "main",
+    "outcome": "Publish honest Docker buildcache estimates: exclude images referenced by containers and preserve unknown reclaimability for shared image layers or missing BuildKit measurements.",
+    "nonGoals": [
+      "No new cleanup effects or Docker volume removal",
+      "No cleanup retention policy changes",
+      "No runtime dependency changes"
+    ],
+    "complexity": "S",
+    "estimatedMinutes": 30,
+    "budgets": {
+      "maxImplementationFiles": 2,
+      "maxAffectedComponents": 1,
+      "maxPublicInterfaceChanges": 1,
+      "maxRuntimeDependencies": 0
+    },
+    "architecture": {
+      "status": "accepted",
+      "decision": "Read full dangling image IDs and container image references; separate aggregate image size from unknown uniquely reclaimable storage.",
+      "components": [
+        {
+          "name": "docker-cleanup-inventory",
+          "paths": [
+            "fixos/cli/_cleanup_space.py",
+            "tests/unit/test_cleanup_docker_buildcache.py"
+          ]
+        }
+      ],
+      "responsibilityChanges": false,
+      "interfaceChanges": [
+        "Return null for unknown reclaimable bytes instead of logical image totals."
+      ],
+      "dataChanges": [],
+      "ui": {
+        "impact": "none",
+        "states": [],
+        "evidence": []
+      },
+      "rollback": "Revert through protected publication; existing Docker prune commands are retained."
+    },
+    "runtimeDependencies": [],
+    "validation": [
+      {
+        "criterion": "AC-01",
+        "commands": [
+          "python -m pytest tests/unit/test_cleanup_docker_buildcache.py -q",
+          "python -m ruff check --select I fixos/cli/_cleanup_space.py tests/unit/test_cleanup_docker_buildcache.py",
+          "./project/governance-check.sh"
+        ],
+        "evidence": "project/ticket-113/README.md"
+      }
+    ]
+  }
+}
diff --git a/tests/unit/test_cleanup_docker_buildcache.py b/tests/unit/test_cleanup_docker_buildcache.py
new file mode 100644
index 0000000..86dfdc9
--- /dev/null
+++ b/tests/unit/test_cleanup_docker_buildcache.py
@@ -0,0 +1,103 @@
+"""Docker cleanup estimates must distinguish logical size from reclaimability."""
+
+import subprocess
+
+import pytest
+from click.testing import CliRunner
+
+from fixos.cli import _cleanup_space as cleanup
+
+IMAGE_A = "sha256:" + "a" * 64
+IMAGE_B = "sha256:" + "b" * 64
+CONTAINER = "c" * 64
+
+
+def stub_docker(monkeypatch, *, containers="", inspected="", failure=None):
+    calls = []
+
+    def run(argv, timeout=60):
+        calls.append(argv)
+        if argv[:2] == ["docker", "images"]:
+            output = f"{IMAGE_A}\t7GB\n{IMAGE_B}\t7GB\n"
+        elif argv[:3] == ["docker", "container", "ls"]:
+            output = containers
+        elif argv[:3] == ["docker", "container", "inspect"]:
+            if failure is not None:
+                if isinstance(failure, Exception):
+                    raise failure
+                return subprocess.CompletedProcess(argv, failure, "", "unavailable")
+            output = inspected
+        else:
+            raise AssertionError(argv)
+        return subprocess.CompletedProcess(argv, 0, output, "")
+
+    monkeypatch.setattr(cleanup, "_run_cmd", run)
+    return calls
+
+
+def test_images_referenced_by_any_container_are_excluded(monkeypatch):
+    calls = stub_docker(monkeypatch, containers=CONTAINER + "\n", inspected=IMAGE_A + "\n")
+    result = cleanup._dangling_images()
+    assert result["count"] == 1
+    assert result["bytes"] == 7_000_000_000
+    assert result["usage_known"] is True
+    assert ["docker", "container", "ls", "--all", "--quiet", "--no-trunc"] in calls
+    assert any("--no-trunc" in argv for argv in calls if argv[1] == "images")
+
+
+@pytest.mark.parametrize("failure", [1, OSError("unavailable"), subprocess.TimeoutExpired("docker", 60)])
+def test_failed_container_inspection_keeps_usage_unknown(monkeypatch, failure):
+    stub_docker(monkeypatch, containers=CONTAINER + "\n", failure=failure)
+    result = cleanup._dangling_images()
+    assert result["usage_known"] is False
+    assert result["count"] == 2
+
+
+def test_no_containers_needs_no_inspection(monkeypatch):
+    calls = stub_docker(monkeypatch)
+    result = cleanup._dangling_images()
+    assert result["usage_known"] is True
+    assert result["count"] == 2
+    assert not any("inspect" in argv for argv in calls)
+
+
+def test_image_totals_do_not_claim_shared_layers_as_reclaimable(monkeypatch):
+    stub_docker(monkeypatch)
+    monkeypatch.setattr(cleanup, "_docker_buildx_builders", list)
+    target = cleanup._docker_buildcache_scan()["targets"][0]
+    assert target["total_bytes"] == 14_000_000_000
+    assert target["reclaimable_bytes"] is None
+    assert target["command"] == ["docker", "image", "prune", "--force"]
+
+
+def test_all_referenced_images_produce_no_prune_target(monkeypatch):
+    stub_docker(monkeypatch, containers=f"{CONTAINER}\n{'d' * 64}\n", inspected=f"{IMAGE_A}\n{IMAGE_B}\n")
+    monkeypatch.setattr(cleanup, "_docker_buildx_builders", list)
+    assert cleanup._docker_buildcache_scan()["targets"] == []
+
+
+def test_missing_builder_reclaimable_measurement_is_unknown(monkeypatch):
+    monkeypatch.setattr(cleanup, "_run_cmd", lambda argv, **kw: subprocess.CompletedProcess(argv, 0, "Total: 14GB\n", ""))
+    assert cleanup._builder_cache_bytes("default") == (14_000_000_000, None)
+
+
+def test_measured_zero_reclaimable_stays_zero(monkeypatch):
+    monkeypatch.setattr(cleanup, "_run_cmd", lambda argv, **kw: subprocess.CompletedProcess(argv, 0, "Reclaimable: 0B\nTotal: 14GB\n", ""))
+    assert cleanup._builder_cache_bytes("default") == (14_000_000_000, 0)
+
+
+def test_cli_labels_unknown_reclaimability(monkeypatch):
+    import click
+
+    stub_docker(monkeypatch)
+    monkeypatch.setattr(cleanup, "_docker_buildx_builders", list)
+
+    @click.command()
+    def command():
+        cleanup._cleanup_docker_buildcache(False, True, False, False)
+
+    result = CliRunner().invoke(command)
+    assert result.exit_code == 0, result.output
+    assert "odzyskiwalny rozmiar nieznany" in result.output
+    assert "suma rozmiarów obrazów" in result.output
+    assert "docker image prune --force" in result.output