diff --git a/README.md b/README.md
index fd08045..5f9a46e 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,7 @@ versioning features it can drive **end-to-end workflows**:
 | `pkgmgr branch cleanup [--apply]` | Removes merged branches that no worktree holds, locally and on the remotes |
 | `pkgmgr branch tree [--format json\|yaml] [--output FILE]` | Writes every managed repository's branches and worktrees with their cleanup state, without fetching |
 | `pkgmgr gc [--all] [--apply]` | Both cleanups in one pass, for the current repository or every managed one |
+| `pkgmgr gc --report [--all] [--root DIR] [--threshold-mb MB] [--docker] [--json]` | Read-only disk inventory: worktree sizes, changes a cleanup would keep, `--root` children, core dumps, docker usage, free space per filesystem |
 | `pkgmgr worktree orphans --stale-days N --top N` | Lists merged and abandoned branches and worktrees with a proposal each |
 
 A hook runs only when the `worktree_hooks` config pins its command under the
diff --git a/src/pkgmgr/actions/gc/__init__.py b/src/pkgmgr/actions/gc/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/pkgmgr/actions/gc/report/__init__.py b/src/pkgmgr/actions/gc/report/__init__.py
new file mode 100644
index 0000000..640f66b
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/__init__.py
@@ -0,0 +1,4 @@
+from .render import render_text
+from .report import disk_report
+
+__all__ = ["disk_report", "render_text"]
diff --git a/src/pkgmgr/actions/gc/report/balance.py b/src/pkgmgr/actions/gc/report/balance.py
new file mode 100644
index 0000000..7c4a9e1
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/balance.py
@@ -0,0 +1,54 @@
+from __future__ import annotations
+
+import os
+
+from pkgmgr.actions.branch.gc import _inside
+
+
+def _mount(path: str) -> str:
+    path = os.path.realpath(path)
+    while not os.path.ismount(path):
+        path = os.path.dirname(path)
+    return path
+
+
+def balance(paths: list[str], items: list[tuple[str, int]]) -> list[dict]:
+    """
+    Set what the report attributes against each filesystem's capacity.
+
+    Args:
+        paths: the roots and repository roots; each one's filesystem gets a row.
+        items: (path, allocated bytes) of every listed entry; an entry inside
+            another listed entry is counted only through the outer one.
+
+    Returns:
+        Per filesystem (grouped by st_dev): its mount point, total and free
+        bytes (as available to unprivileged users) and the attributed bytes.
+    """
+    filesystems: dict[int, dict] = {}
+    for path in paths:
+        try:
+            dev = os.stat(path).st_dev
+            if dev in filesystems:
+                continue
+            vfs = os.statvfs(path)
+        except OSError:
+            continue
+        filesystems[dev] = {
+            "filesystem": _mount(path),
+            "total_bytes": vfs.f_blocks * vfs.f_frsize,
+            "free_bytes": vfs.f_bavail * vfs.f_frsize,
+            "attributed_bytes": 0,
+        }
+    kept: list[str] = []
+    for path, size in sorted((os.path.realpath(p), s) for p, s in items):
+        if any(_inside(path, outer) for outer in kept):
+            continue
+        kept.append(path)
+        try:
+            dev = os.lstat(path).st_dev
+        except OSError:
+            continue
+        if dev in filesystems:
+            filesystems[dev]["attributed_bytes"] += size
+    return sorted(filesystems.values(), key=lambda fs: fs["filesystem"])
diff --git a/src/pkgmgr/actions/gc/report/core_dumps.py b/src/pkgmgr/actions/gc/report/core_dumps.py
new file mode 100644
index 0000000..de5cfdf
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/core_dumps.py
@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import os
+
+from .walk import BLOCK
+
+ELF_MAGIC = b"\x7fELF"
+ELF_HEADER = 18
+ET_CORE = 4
+BYTE_ORDER = {1: "little", 2: "big"}
+
+
+def is_core_dump(path: str) -> bool:
+    try:
+        fd = os.open(path, os.O_RDONLY | os.O_NOFOLLOW | os.O_NONBLOCK)
+    except OSError:
+        return False
+    try:
+        head = os.read(fd, ELF_HEADER)
+    except OSError:
+        return False
+    finally:
+        os.close(fd)
+    order = BYTE_ORDER.get(head[5]) if len(head) == ELF_HEADER else None
+    return (
+        head[:4] == ELF_MAGIC
+        and order is not None
+        and int.from_bytes(head[16:18], order) == ET_CORE
+    )
+
+
+def core_dumps(candidates: list[str]) -> list[dict]:
+    """
+    Keep the candidates whose ELF header says ET_CORE.
+
+    Args:
+        candidates: paths of regular files named like core dumps.
+
+    Returns:
+        One entry per dump with its allocated and apparent size and mtime,
+        biggest first.
+    """
+    dumps: dict[str, dict] = {}
+    for path in candidates:
+        real = os.path.realpath(path)
+        if real in dumps or not is_core_dump(path):
+            continue
+        try:
+            st = os.lstat(path)
+        except OSError:
+            continue
+        dumps[real] = {
+            "path": path,
+            "size_bytes": st.st_blocks * BLOCK,
+            "apparent_bytes": st.st_size,
+            "mtime": st.st_mtime,
+        }
+    return sorted(dumps.values(), key=lambda d: (-d["size_bytes"], d["path"]))
diff --git a/src/pkgmgr/actions/gc/report/docker_usage.py b/src/pkgmgr/actions/gc/report/docker_usage.py
new file mode 100644
index 0000000..4eb6d67
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/docker_usage.py
@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+import json
+import subprocess
+
+from pkgmgr.actions.branch.gc import _describe, _docker
+
+DF_ARGS = ["system", "df", "--format", "{{json .}}"]
+
+
+def _count(value: object) -> int | None:
+    text = str(value)
+    return int(text) if text.isdigit() else None
+
+
+def docker_usage() -> tuple[list[dict] | None, str | None]:
+    """
+    Read `docker system df` per type.
+
+    Returns:
+        The rows (type, total and active counts, size and reclaimable as docker
+        prints them) and None, or None and a warning when docker is missing,
+        fails or prints something else than JSON lines.
+    """
+    try:
+        out = _docker(DF_ARGS)
+    except FileNotFoundError:
+        return None, "docker unavailable: not installed"
+    except subprocess.CalledProcessError as exc:
+        return None, f"docker unavailable: {_describe(exc)}"
+    rows: list[dict] = []
+    for line in out.splitlines():
+        if not line.strip():
+            continue
+        try:
+            data = json.loads(line)
+        except ValueError:
+            data = None
+        if not isinstance(data, dict):
+            return None, "docker system df: output is not JSON lines"
+        rows.append(
+            {
+                "type": data.get("Type"),
+                "total": _count(data.get("TotalCount")),
+                "active": _count(data.get("Active")),
+                "size": data.get("Size"),
+                "reclaimable": data.get("Reclaimable"),
+            }
+        )
+    return rows, None
diff --git a/src/pkgmgr/actions/gc/report/preserved.py b/src/pkgmgr/actions/gc/report/preserved.py
new file mode 100644
index 0000000..78698cb
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/preserved.py
@@ -0,0 +1,186 @@
+from __future__ import annotations
+
+import os
+import stat
+
+from pkgmgr.actions.branch.gc import _describe, _git, _has_submodules
+from pkgmgr.core.git.errors import GitBaseError
+from pkgmgr.core.git.queries import FILTER_CONFIG, local_config
+from pkgmgr.core.git.run import run
+
+REF_NAMESPACES = ("refs/heads", "refs/remotes", "refs/tags")
+PEELED = "%(if)%(*objectname)%(then)%(*objectname)%(else)%(objectname)%(end)"
+UNMERGED = "unmerged"
+DELETED = "deleted"
+DIRECTORY = "directory"
+SPECIAL = "special"
+UNHASHABLE = {
+    DIRECTORY: "untracked directory or gitlink",
+    SPECIAL: "not a regular file",
+}
+MAX_REASONS = 5
+
+
+def _tips(repo: str) -> list[str]:
+    out = _git(["for-each-ref", f"--format={PEELED}", *REF_NAMESPACES], repo)
+    return sorted(set(out.split()))
+
+
+def _status_entries(tree: str) -> list[tuple[str, str | None]]:
+    raw = _git(
+        [
+            "status",
+            "--porcelain=v2",
+            "-z",
+            "--untracked-files=all",
+            "--no-renames",
+        ],
+        tree,
+    )
+    entries: list[tuple[str, str | None]] = []
+    for record in raw.split("\0"):
+        kind = record[:1]
+        if kind == "1":
+            parts = record.split(" ", 8)
+            entries.append((parts[8], parts[7]))
+        elif kind == "u":
+            entries.append((record.split(" ", 10)[10], UNMERGED))
+        elif kind == "?":
+            entries.append((record[2:], None))
+    return entries
+
+
+def _hashes(tree: str, paths: list[str]) -> dict[str, str]:
+    hashes: dict[str, str] = {}
+    files: list[str] = []
+    for path in paths:
+        full = os.path.join(tree, path)
+        try:
+            mode = os.lstat(full).st_mode
+        except FileNotFoundError:
+            hashes[path] = DELETED
+            continue
+        if stat.S_ISREG(mode):
+            files.append(path)
+        elif stat.S_ISLNK(mode):
+            hashes[path] = run(
+                ["hash-object", "-t", "blob", "--no-filters", "--stdin"],
+                cwd=tree,
+                scan=True,
+                input_text=os.readlink(full),
+            )
+        else:
+            hashes[path] = DIRECTORY if stat.S_ISDIR(mode) else SPECIAL
+    if files:
+        out = run(
+            ["hash-object", "--no-filters", "--stdin-paths"],
+            cwd=tree,
+            scan=True,
+            input_text="".join(f"{path}\n" for path in files),
+        )
+        hashes.update(zip(files, out.split("\n")))
+    return hashes
+
+
+def _absent(
+    repo: str, tips: list[str], wanted: list[tuple[str, set[str]]]
+) -> list[str]:
+    query = "".join(f"{tip}:{path}\n" for path, _ in wanted for tip in tips)
+    if not query:
+        return [path for path, _ in wanted]
+    found = run(
+        ["cat-file", "--batch-check=%(objectname)"],
+        cwd=repo,
+        scan=True,
+        input_text=query,
+    ).split("\n")
+    width = len(tips)
+    return [
+        path
+        for index, (path, blobs) in enumerate(wanted)
+        if blobs - set(found[index * width : (index + 1) * width])
+    ]
+
+
+def _reachable(repo: str, head: str | None) -> bool:
+    if not head:
+        return False
+    return bool(
+        _git(["for-each-ref", "--count=1", f"--contains={head}", *REF_NAMESPACES], repo)
+    )
+
+
+def _unpreserved(
+    repo: str, record: dict, tips: list[str]
+) -> tuple[int | None, list[str]]:
+    tree = record["path"]
+    if _has_submodules(tree):
+        return None, ["submodules, whose config the scan cannot vet"]
+    unsafe = local_config(tree, FILTER_CONFIG)
+    if unsafe:
+        return None, [f"{', '.join(unsafe)} in the repository config"]
+    entries = _status_entries(tree)
+    reasons: list[str] = []
+    if entries and record["branch"] is None and not _reachable(repo, record["head"]):
+        reasons.append("detached HEAD reachable from no ref")
+    hashable: list[tuple[str, str | None]] = []
+    for path, index_blob in entries:
+        if "\n" in path:
+            reasons.append(f"{path!r}: path with a newline")
+        elif index_blob == UNMERGED:
+            reasons.append(f"{path}: unmerged")
+        else:
+            hashable.append((path, index_blob))
+    hashes = _hashes(tree, [path for path, _ in hashable])
+    wanted: list[tuple[str, set[str]]] = []
+    for path, index_blob in hashable:
+        current = hashes[path]
+        if current in UNHASHABLE:
+            reasons.append(f"{path}: {UNHASHABLE[current]}")
+            continue
+        blobs = {current} - {DELETED}
+        if index_blob and set(index_blob) != {"0"}:
+            blobs.add(index_blob)
+        if blobs:
+            wanted.append((path, blobs))
+    reasons += [f"{path}: content in no ref" for path in _absent(repo, tips, wanted)]
+    return len(entries), reasons
+
+
+def preserved(repo: str, records: list[dict]) -> list[dict]:
+    """
+    Decide for each dirty worktree whether all its work survives its deletion.
+
+    Args:
+        repo: main worktree root of the repository.
+        records: its worktree records from list_worktrees.
+
+    Returns:
+        One entry per dirty or unreadable worktree; `preserved` is true only
+        when every changed, staged and untracked file's content is a blob at
+        the same path of some branch, remote or tag tip, and a detached HEAD is
+        reachable from a ref. `reasons` lists what is not, capped.
+    """
+    live = [r for r in records if not r["orphaned"] and not r["missing"]]
+    tips = _tips(repo) if live else []
+    results: list[dict] = []
+    for record in live:
+        try:
+            paths, reasons = _unpreserved(repo, record, tips)
+        except (GitBaseError, OSError, UnicodeError) as exc:
+            paths, reasons = None, [f"status failed: {_describe(exc)}"]
+        if paths == 0:
+            continue
+        extra = len(reasons) - MAX_REASONS
+        results.append(
+            {
+                "repo": repo,
+                "path": record["path"],
+                "branch": record["branch"],
+                "paths": paths,
+                "preserved": not reasons,
+                "reasons": reasons[:MAX_REASONS]
+                + ([f"... {extra} more"] if extra > 0 else []),
+            }
+        )
+    return results
diff --git a/src/pkgmgr/actions/gc/report/render.py b/src/pkgmgr/actions/gc/report/render.py
new file mode 100644
index 0000000..a776fa4
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/render.py
@@ -0,0 +1,132 @@
+from __future__ import annotations
+
+from pkgmgr.actions.branch.gc import human_size
+
+UNITS = (("d", 86400), ("h", 3600), ("m", 60))
+DOCKER_COLUMNS = ("type", "total", "active", "size", "reclaimable")
+
+
+def _size(value: int | None) -> str:
+    return "-" if value is None else human_size(value)
+
+
+def _age(now: float, stamp: float | None) -> str:
+    if not stamp:
+        return "-"
+    seconds = max(0.0, now - stamp)
+    for unit, length in UNITS:
+        if seconds >= length:
+            return f"{seconds / length:.1f}{unit}"
+    return f"{seconds:.0f}s"
+
+
+def _section(title: str, headers: list[str], rows: list[list[str]]) -> list[str]:
+    if not rows:
+        return [f"== {title}", "(none)"]
+    widths = [max(len(cell) for cell in column) for column in zip(headers, *rows)]
+    return [f"== {title}"] + [
+        "  ".join(cell.ljust(width) for cell, width in zip(row, widths)).rstrip()
+        for row in (headers, *rows)
+    ]
+
+
+def _branch(tree: dict) -> str:
+    if tree["orphaned"]:
+        return "-"
+    return tree["branch"] or "(detached)"
+
+
+def _state(tree: dict) -> str:
+    if tree["orphaned"]:
+        return "orphaned"
+    return "missing" if tree["missing"] else "linked"
+
+
+def render_text(report: dict) -> str:
+    """
+    Render a disk_report result as aligned text tables.
+
+    Args:
+        report: the dict disk_report returned.
+
+    Returns:
+        The tables, one section per report key, newline-joined.
+    """
+    now = report["generated_at"]
+    lines = _section(
+        "worktrees",
+        ["SIZE", "ACTIVE", "FOREIGN", "STATE", "BRANCH", "PATH"],
+        [
+            [
+                _size(t["size_bytes"]),
+                _age(now, t["last_activity"]),
+                str(t["foreign_entries"]),
+                _state(t),
+                _branch(t),
+                t["path"],
+            ]
+            for t in report["worktrees"]
+        ],
+    )
+    lines += _section(
+        "preserved (dirty worktrees)",
+        ["PRESERVED", "PATHS", "BRANCH", "PATH", "REASONS"],
+        [
+            [
+                "yes" if p["preserved"] else "no",
+                "-" if p["paths"] is None else str(p["paths"]),
+                p["branch"] or "(detached)",
+                p["path"],
+                "; ".join(p["reasons"]),
+            ]
+            for p in report["preserved"]
+        ],
+    )
+    for root in report["roots"]:
+        lines += _section(
+            f"root {root['root']} (over {human_size(report['threshold_bytes'])})",
+            ["SIZE", "AGE", "KIND", "PATH"],
+            [
+                [
+                    _size(c["size_bytes"]),
+                    _age(now, c["newest_mtime"]),
+                    c["kind"],
+                    c["path"],
+                ]
+                for c in root["children"]
+            ],
+        )
+    lines += _section(
+        "core dumps",
+        ["SIZE", "APPARENT", "AGE", "PATH"],
+        [
+            [
+                _size(d["size_bytes"]),
+                _size(d["apparent_bytes"]),
+                _age(now, d["mtime"]),
+                d["path"],
+            ]
+            for d in report["core_dumps"]
+        ],
+    )
+    if report["docker"] is not None:
+        lines += _section(
+            "docker",
+            ["TYPE", "TOTAL", "ACTIVE", "SIZE", "RECLAIMABLE"],
+            [[str(row[key]) for key in DOCKER_COLUMNS] for row in report["docker"]],
+        )
+    lines += _section(
+        "balance",
+        ["FILESYSTEM", "TOTAL", "FREE", "ATTRIBUTED"],
+        [
+            [
+                fs["filesystem"],
+                _size(fs["total_bytes"]),
+                _size(fs["free_bytes"]),
+                _size(fs["attributed_bytes"]),
+            ]
+            for fs in report["balance"]
+        ],
+    )
+    lines += [f"WARN  {warning}" for warning in report["warnings"]]
+    return "\n".join(lines)
diff --git a/src/pkgmgr/actions/gc/report/report.py b/src/pkgmgr/actions/gc/report/report.py
new file mode 100644
index 0000000..f555437
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/report.py
@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+import time
+
+from pkgmgr.actions.branch.gc import _describe
+from pkgmgr.core.git.errors import GitBaseError
+
+from .balance import balance
+from .core_dumps import core_dumps
+from .docker_usage import docker_usage
+from .preserved import preserved
+from .roots import scan_root
+from .worktrees import list_worktrees
+
+
+def disk_report(
+    roots: list[str], repo_roots: list[str], threshold_bytes: int, docker: bool
+) -> dict:
+    """
+    Inventory disk usage read-only: it deletes and writes nothing.
+
+    Args:
+        roots: directories whose direct children are measured.
+        repo_roots: main worktree roots of the repositories whose linked
+            worktrees are listed (pkgmgr passes every managed repository).
+        threshold_bytes: list only root children larger than this.
+        docker: also read `docker system df`.
+
+    Returns:
+        A JSON-serialisable dict. Sizes are allocated bytes (st_blocks * 512,
+        sparse files and hard links counted as stored), measured without
+        following symlinks or leaving the filesystem a walk starts on; times
+        are epoch seconds.
+            generated_at: when the scan started.
+            threshold_bytes: as given.
+            worktrees: per linked worktree and orphaned `.claude/worktrees/agent-*`
+                dir: repo, path, branch, head, orphaned, missing, size_bytes,
+                last_activity (newest mtime inside or of its index/HEAD),
+                foreign_entries (not owned by the current uid, pruned at the first
+                per subtree), unreadable (directories that could not be listed).
+            preserved: per dirty worktree: repo, path, branch, paths (changed,
+                staged and untracked; None when status was not read), preserved,
+                reasons.
+            roots: per root: root, children over the threshold with path, kind
+                (worktree, git-repo, venv, node_modules, cache, core-dump, dir,
+                file), size_bytes, newest_mtime, unreadable; biggest first.
+            core_dumps: files named `core` or `core.<digits>` under the roots and
+                worktrees whose ELF e_type is ET_CORE: path, size_bytes,
+                apparent_bytes (st_size), mtime; biggest first.
+            docker: rows of type, total, active, size, reclaimable; None when not
+                asked for or unavailable.
+            balance: per filesystem of the roots and repository roots: filesystem
+                (mount point), total_bytes, free_bytes, attributed_bytes.
+            warnings: what could not be read.
+    """
+    started = time.time()
+    warnings: list[str] = []
+    cores: list[str] = []
+    trees: list[dict] = []
+    kept: list[dict] = []
+    for repo in repo_roots:
+        try:
+            records = list_worktrees(repo, cores)
+        except (GitBaseError, OSError) as exc:
+            warnings.append(f"{repo}: worktrees not listed: {_describe(exc)}")
+            continue
+        trees += records
+        try:
+            kept += preserved(repo, records)
+        except (GitBaseError, OSError) as exc:
+            warnings.append(f"{repo}: preservation not checked: {_describe(exc)}")
+    scanned: list[dict] = []
+    for root in roots:
+        try:
+            scanned.append(scan_root(root, threshold_bytes, cores))
+        except OSError as exc:
+            warnings.append(f"{root}: not scanned: {_describe(exc)}")
+    dumps = core_dumps(cores)
+    usage = None
+    if docker:
+        usage, warning = docker_usage()
+        if warning:
+            warnings.append(warning)
+    items = [(t["path"], t["size_bytes"]) for t in trees if t["size_bytes"]]
+    items += [(c["path"], c["size_bytes"]) for s in scanned for c in s["children"]]
+    items += [(d["path"], d["size_bytes"]) for d in dumps]
+    return {
+        "generated_at": started,
+        "threshold_bytes": threshold_bytes,
+        "worktrees": trees,
+        "preserved": kept,
+        "roots": scanned,
+        "core_dumps": dumps,
+        "docker": usage,
+        "balance": balance([*roots, *repo_roots], items),
+        "warnings": warnings,
+    }
diff --git a/src/pkgmgr/actions/gc/report/roots.py b/src/pkgmgr/actions/gc/report/roots.py
new file mode 100644
index 0000000..45b2d19
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/roots.py
@@ -0,0 +1,77 @@
+from __future__ import annotations
+
+import os
+import stat
+
+from .core_dumps import is_core_dump
+from .walk import walk
+
+CACHE_TAG = "CACHEDIR.TAG"
+NODE_MODULES = "node_modules"
+
+
+def _has(path: str, name: str, check=os.path.isfile) -> bool:
+    return check(os.path.join(path, name))
+
+
+def _kind(path: str, st: os.stat_result) -> str:
+    name = os.path.basename(path)
+    if not stat.S_ISDIR(st.st_mode):
+        regular = stat.S_ISREG(st.st_mode)
+        return "core-dump" if regular and is_core_dump(path) else "file"
+    if name == NODE_MODULES:
+        return "node_modules"
+    if _has(path, ".git"):
+        return "worktree"
+    if _has(path, ".git", os.path.isdir) or (
+        _has(path, "HEAD") and _has(path, "objects", os.path.isdir)
+    ):
+        return "git-repo"
+    if _has(path, "pyvenv.cfg"):
+        return "venv"
+    if _has(path, CACHE_TAG) or name.lower().endswith("cache"):
+        return "cache"
+    return "dir"
+
+
+def scan_root(root: str, threshold_bytes: int, cores: list[str]) -> dict:
+    """
+    Measure the direct children of one root on the root's own filesystem.
+
+    Args:
+        root: the directory to inventory.
+        threshold_bytes: keep only children whose allocated size is above it.
+        cores: receives the core dump candidates found while measuring.
+
+    Returns:
+        The root with its children over the threshold: path, kind, allocated
+        size, newest mtime inside and unlistable directories, biggest first.
+
+    Raises:
+        OSError: when the root itself cannot be listed.
+    """
+    dev = os.stat(root).st_dev
+    children: list[dict] = []
+    with os.scandir(root) as entries:
+        listing = sorted(entries, key=lambda entry: entry.name)
+    for entry in listing:
+        try:
+            st = entry.stat(follow_symlinks=False)
+        except OSError:
+            continue
+        if st.st_dev != dev:
+            continue
+        stats = walk(entry.path, dev)
+        cores.extend(stats.cores)
+        if stats.size_bytes > threshold_bytes:
+            children.append(
+                {
+                    "path": entry.path,
+                    "kind": _kind(entry.path, st),
+                    "size_bytes": stats.size_bytes,
+                    "newest_mtime": stats.newest_mtime,
+                    "unreadable": stats.unreadable,
+                }
+            )
+    children.sort(key=lambda child: (-child["size_bytes"], child["path"]))
+    return {"root": root, "children": children}
diff --git a/src/pkgmgr/actions/gc/report/walk.py b/src/pkgmgr/actions/gc/report/walk.py
new file mode 100644
index 0000000..11c6595
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/walk.py
@@ -0,0 +1,86 @@
+from __future__ import annotations
+
+import os
+import re
+import stat
+from dataclasses import dataclass, field
+
+BLOCK = 512
+CORE_NAME = re.compile(r"core(\.\d+)?")
+
+
+@dataclass
+class TreeStats:
+    size_bytes: int = 0
+    newest_mtime: float = 0.0
+    foreign_entries: int = 0
+    unreadable: int = 0
+    cores: list[str] = field(default_factory=list)
+
+
+def is_foreign(path: str, st: os.stat_result) -> bool:
+    return st.st_uid != os.getuid()
+
+
+def _account(
+    stats: TreeStats, path: str, st: os.stat_result, seen: set[tuple[int, int]]
+) -> None:
+    if st.st_nlink > 1 and not stat.S_ISDIR(st.st_mode):
+        if (st.st_dev, st.st_ino) in seen:
+            return
+        seen.add((st.st_dev, st.st_ino))
+    stats.size_bytes += st.st_blocks * BLOCK
+    stats.newest_mtime = max(stats.newest_mtime, st.st_mtime)
+    if stat.S_ISREG(st.st_mode) and CORE_NAME.fullmatch(os.path.basename(path)):
+        stats.cores.append(path)
+
+
+def _children(path: str, stats: TreeStats) -> list[os.DirEntry]:
+    try:
+        with os.scandir(path) as entries:
+            return list(entries)
+    except OSError:
+        stats.unreadable += 1
+        return []
+
+
+def walk(path: str, dev: int | None = None) -> TreeStats:
+    """
+    Measure a tree like `du -x`: allocated blocks, symlinks never followed.
+
+    Args:
+        path: the tree root, measured itself as well.
+        dev: the filesystem (st_dev) to stay on; that of path when None.
+
+    Returns:
+        Allocated bytes (st_blocks * 512, each hard-linked inode once), the
+        newest mtime, entries not owned by the current uid (none counted below a
+        foreign one), directories that could not be listed, and the regular
+        files named `core` or `core.<digits>`.
+    """
+    stats = TreeStats()
+    try:
+        top = os.lstat(path)
+    except OSError:
+        stats.unreadable += 1
+        return stats
+    dev = top.st_dev if dev is None else dev
+    if top.st_dev != dev:
+        return stats
+    seen: set[tuple[int, int]] = set()
+    stack: list[tuple[str, os.stat_result, bool]] = [(path, top, False)]
+    while stack:
+        current, st, pruned = stack.pop()
+        _account(stats, current, st, seen)
+        foreign = not pruned and is_foreign(current, st)
+        stats.foreign_entries += foreign
+        if not stat.S_ISDIR(st.st_mode):
+            continue
+        for entry in _children(current, stats):
+            try:
+                child = entry.stat(follow_symlinks=False)
+            except OSError:
+                continue
+            if child.st_dev == dev:
+                stack.append((entry.path, child, pruned or foreign))
+    return stats
diff --git a/src/pkgmgr/actions/gc/report/worktrees.py b/src/pkgmgr/actions/gc/report/worktrees.py
new file mode 100644
index 0000000..1748b7a
--- /dev/null
+++ b/src/pkgmgr/actions/gc/report/worktrees.py
@@ -0,0 +1,96 @@
+from __future__ import annotations
+
+import os
+
+from pkgmgr.actions.branch.gc import _worktrees
+
+from .walk import TreeStats, walk
+
+AGENT_DIR = os.path.join(".claude", "worktrees")
+AGENT_PREFIX = "agent-"
+METADATA_FILES = ("index", "HEAD")
+
+
+def _metadata_mtime(path: str) -> float:
+    try:
+        with open(os.path.join(path, ".git"), encoding="utf-8") as fh:
+            gitdir = fh.read().strip().removeprefix("gitdir: ")
+    except OSError:
+        return 0.0
+    meta = os.path.normpath(os.path.join(path, gitdir))
+    stamps = [0.0]
+    for name in METADATA_FILES:
+        try:
+            stamps.append(os.stat(os.path.join(meta, name)).st_mtime)
+        except OSError:
+            continue
+    return max(stamps)
+
+
+def _record(
+    repo: str,
+    path: str,
+    branch: str | None,
+    head: str | None,
+    orphaned: bool,
+    cores: list[str],
+) -> dict:
+    present = os.path.isdir(path)
+    stats = walk(path) if present else TreeStats()
+    cores.extend(stats.cores)
+    activity = max(stats.newest_mtime, _metadata_mtime(path)) if present else 0.0
+    return {
+        "repo": repo,
+        "path": path,
+        "branch": branch,
+        "head": head,
+        "orphaned": orphaned,
+        "missing": not present,
+        "size_bytes": stats.size_bytes if present else None,
+        "last_activity": activity or None,
+        "foreign_entries": stats.foreign_entries,
+        "unreadable": stats.unreadable,
+    }
+
+
+def _agent_dirs(repo: str) -> list[str]:
+    base = os.path.join(repo, AGENT_DIR)
+    try:
+        names = sorted(os.listdir(base))
+    except OSError:
+        return []
+    return [
+        os.path.join(base, name)
+        for name in names
+        if name.startswith(AGENT_PREFIX)
+        and os.path.isdir(os.path.join(base, name))
+        and not os.path.islink(os.path.join(base, name))
+    ]
+
+
+def list_worktrees(repo: str, cores: list[str]) -> list[dict]:
+    """
+    Inventory the linked worktrees of one repository, orphaned agent dirs included.
+
+    Args:
+        repo: main worktree root of the repository.
+        cores: receives the core dump candidates found while measuring.
+
+    Returns:
+        One record per linked worktree git lists and per `.claude/worktrees/agent-*`
+        directory it does not list (orphaned), sorted by path.
+
+    Raises:
+        GitBaseError: when `git worktree list` fails.
+    """
+    trees = [tree for tree in _worktrees(repo) if not tree.main]
+    listed = {os.path.realpath(tree.path) for tree in trees}
+    records = [
+        _record(repo, tree.path, tree.branch, tree.head, False, cores) for tree in trees
+    ]
+    records += [
+        _record(repo, path, None, None, True, cores)
+        for path in _agent_dirs(repo)
+        if os.path.realpath(path) not in listed
+    ]
+    return sorted(records, key=lambda record: record["path"])
diff --git a/src/pkgmgr/cli/commands/worktree.py b/src/pkgmgr/cli/commands/worktree.py
index 64c9ff0..049afce 100644
--- a/src/pkgmgr/cli/commands/worktree.py
+++ b/src/pkgmgr/cli/commands/worktree.py
@@ -1,8 +1,11 @@
 from __future__ import annotations
 
+import json
+import os
 import sys
 
 from pkgmgr.actions.branch.gc import main_repo_root
+from pkgmgr.actions.gc.report import disk_report, render_text
 from pkgmgr.actions.worktree.orphans import worktree_orphans
 from pkgmgr.actions.worktree.up import worktree_up
 from pkgmgr.cli.context import CLIContext
@@ -15,6 +18,8 @@ from .branch import (
     scan_repo_roots,
 )
 
+MEBIBYTE = 1 << 20
+
 
 def handle_worktree(args, ctx: CLIContext) -> None:
     """
@@ -56,4 +61,18 @@ def handle_worktree(args, ctx: CLIContext) -> None:
 
 
 def handle_gc(args, ctx: CLIContext) -> None:
-    run_cleanup(args, ctx, "all")
+    if not args.report:
+        run_cleanup(args, ctx, "all")
+    if args.apply:
+        print(
+            "--report only reads; it cannot be combined with --apply", file=sys.stderr
+        )
+        sys.exit(2)
+    report = disk_report(
+        [os.path.abspath(os.path.expanduser(root)) for root in args.root],
+        scan_repo_roots(args, ctx),
+        args.threshold_mb * MEBIBYTE,
+        args.docker,
+    )
+    print(json.dumps(report, indent=2) if args.json else render_text(report))
+    sys.exit(0)
diff --git a/src/pkgmgr/cli/parser/gc_cmd.py b/src/pkgmgr/cli/parser/gc_cmd.py
index a8e30c7..e2bb44f 100644
--- a/src/pkgmgr/cli/parser/gc_cmd.py
+++ b/src/pkgmgr/cli/parser/gc_cmd.py
@@ -16,3 +16,31 @@ def add_gc_subparser(subparsers: argparse._SubParsersAction) -> None:
     add_apply_options(gc)
     add_scan_options(gc)
     add_min_age_option(gc)
+    gc.add_argument(
+        "--report",
+        action="store_true",
+        help=(
+            "Print a read-only disk inventory instead of the cleanup plan: "
+            "worktrees, preserved changes, --root children, core dumps, "
+            "docker usage and free space per filesystem"
+        ),
+    )
+    gc.add_argument(
+        "--root",
+        action="append",
+        default=[],
+        metavar="DIR",
+        help="With --report: also measure the direct children of DIR; repeatable",
+    )
+    gc.add_argument(
+        "--threshold-mb",
+        type=int,
+        default=0,
+        metavar="MB",
+        help="With --report: list only --root children larger than MB (0: all)",
+    )
+    gc.add_argument(
+        "--docker",
+        action="store_true",
+        help="With --report: also read `docker system df`",
+    )
diff --git a/src/pkgmgr/core/git/run.py b/src/pkgmgr/core/git/run.py
index 80d0a94..1a26280 100644
--- a/src/pkgmgr/core/git/run.py
+++ b/src/pkgmgr/core/git/run.py
@@ -58,6 +58,7 @@ def run(
     cwd: str = ".",
     preview: bool = False,
     scan: bool = False,
+    input_text: str | None = None,
 ) -> str:
     """
     Run a Git command and return its stdout as a stripped string.
@@ -69,6 +70,8 @@ def run(
         scan: read a repository an agent may have written: no fsmonitor, hook,
             pager, lazy fetch, replace object, system config or prompt, stdin
             closed, a timeout.
+        input_text: text fed to stdin, e.g. for `cat-file --batch-check`;
+            replaces the closed stdin of scan mode.
 
     Raises GitRunError (or a subclass) if execution fails or times out.
     """
@@ -79,11 +82,14 @@ def run(
         print(f"[PREVIEW] Would run in {cwd!r}: {cmd_str}")
         return ""
 
-    hardened = (
+    hardened: dict = (
         {"env": _scan_env(), "stdin": subprocess.DEVNULL, "timeout": SCAN_TIMEOUT}
         if scan
         else {}
     )
+    if input_text is not None:
+        hardened.pop("stdin", None)
+        hardened["input"] = input_text
     try:
         result = subprocess.run(
             cmd,
diff --git a/tests/integration/test_gc_report.py b/tests/integration/test_gc_report.py
new file mode 100644
index 0000000..38ef99c
--- /dev/null
+++ b/tests/integration/test_gc_report.py
@@ -0,0 +1,215 @@
+from __future__ import annotations
+
+import io
+import json
+import os
+import subprocess
+import tempfile
+import unittest
+from contextlib import redirect_stdout
+from unittest.mock import patch
+
+from pkgmgr.actions.gc.report import disk_report, render_text
+from pkgmgr.actions.gc.report import docker_usage as docker_module
+from pkgmgr.actions.gc.report import walk as walk_module
+from pkgmgr.cli.commands.worktree import handle_gc
+from pkgmgr.cli.parser import create_parser
+
+GIT_ENV = {
+    **os.environ,
+    "GIT_CONFIG_GLOBAL": os.devnull,
+    "GIT_CONFIG_NOSYSTEM": "1",
+    "GIT_AUTHOR_NAME": "t",
+    "GIT_AUTHOR_EMAIL": "t@example.org",
+    "GIT_COMMITTER_NAME": "t",
+    "GIT_COMMITTER_EMAIL": "t@example.org",
+}
+THRESHOLD = 32 * 1024
+ELF_CORE = b"\x7fELF\x02\x01\x01" + bytes(9) + (4).to_bytes(2, "little")
+ELF_EXEC = b"\x7fELF\x02\x01\x01" + bytes(9) + (2).to_bytes(2, "little")
+DOCKER_DF = (
+    '{"Active":"1","Reclaimable":"0B","Size":"1GB","TotalCount":"3","Type":"Images"}\n'
+)
+
+
+def git(cwd: str, *args: str) -> str:
+    return subprocess.run(
+        ["git", *args], cwd=cwd, env=GIT_ENV, check=True, capture_output=True, text=True
+    ).stdout
+
+
+def write(path: str, data: bytes | str, size: int | None = None) -> str:
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "wb") as fh:
+        fh.write(data.encode() if isinstance(data, str) else data)
+    if size is not None:
+        os.truncate(path, size)
+    return path
+
+
+class TestDiskReport(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp = tempfile.TemporaryDirectory()
+        self.tmp = os.path.realpath(self._tmp.name)
+        self.repo = os.path.join(self.tmp, "repo")
+        git(self.tmp, "init", "-q", "-b", "main", self.repo)
+        write(os.path.join(self.repo, "a.txt"), "base")
+        git(self.repo, "add", "a.txt")
+        git(self.repo, "commit", "-q", "-m", "base")
+        git(self.repo, "checkout", "-q", "-b", "other")
+        write(os.path.join(self.repo, "a.txt"), "kept")
+        write(os.path.join(self.repo, "b.txt"), "kept-b")
+        git(self.repo, "add", "a.txt", "b.txt")
+        git(self.repo, "commit", "-q", "-m", "other")
+        git(self.repo, "checkout", "-q", "main")
+
+        self.clean = self._worktree("wt-clean", "-b", "clean")
+        self.kept = self._worktree("wt-kept", "-b", "kept")
+        write(os.path.join(self.kept, "a.txt"), "kept")
+        git(self.kept, "add", "a.txt")
+        write(os.path.join(self.kept, "b.txt"), "kept-b")
+        self.lost = self._worktree("wt-lost", "-b", "lost")
+        write(os.path.join(self.lost, "new.txt"), "only here")
+        self.detached = self._worktree("wt-detached", "--detach")
+        write(os.path.join(self.detached, "c.txt"), "c")
+        git(self.detached, "add", "c.txt")
+        git(self.detached, "commit", "-q", "-m", "unreachable")
+        write(os.path.join(self.detached, "a.txt"), "kept")
+        agents = os.path.join(self.repo, ".claude", "worktrees")
+        self.agent = self._worktree(os.path.join(agents, "agent-y"), "-b", "agent-y")
+        self.orphan = os.path.join(agents, "agent-x")
+        write(os.path.join(self.orphan, "notes.txt"), "left behind")
+
+        self.root = os.path.join(self.tmp, "root")
+        self.dump = write(
+            os.path.join(self.root, "core"), ELF_CORE + b"c" * 64 * 1024, 1 << 30
+        )
+        self.binary = write(
+            os.path.join(self.root, "core.12"), ELF_EXEC + b"e" * 64 * 1024
+        )
+        write(os.path.join(self.root, "bigdir", "blob"), b"b" * 128 * 1024)
+        write(os.path.join(self.root, "small"), "s")
+
+    def tearDown(self) -> None:
+        self._tmp.cleanup()
+
+    def _worktree(self, name: str, *args: str) -> str:
+        path = os.path.join(self.tmp, name)
+        git(self.repo, "worktree", "add", "-q", *args, path, "main")
+        return path
+
+    def _report(self) -> dict:
+        with patch.object(docker_module, "_docker", return_value=DOCKER_DF):
+            return disk_report([self.root], [self.repo], THRESHOLD, docker=True)
+
+    def _cli(self, *argv: str) -> tuple[int, str]:
+        args = create_parser("test").parse_args(["gc", *argv])
+        out = io.StringIO()
+        with (
+            patch("pkgmgr.cli.commands.branch.main_repo_root", return_value=self.repo),
+            patch(
+                "pkgmgr.cli.commands.branch.cleanup",
+                side_effect=AssertionError("the report must not run a cleanup"),
+            ),
+            patch.object(docker_module, "_docker", return_value=DOCKER_DF),
+            redirect_stdout(out),
+            self.assertRaises(SystemExit) as stop,
+        ):
+            handle_gc(args, None)
+        return stop.exception.code, out.getvalue()
+
+    def test_cli_report_prints_the_json_inventory(self) -> None:
+        code, out = self._cli("--report", "--json", "--root", self.root, "--docker")
+        report = json.loads(out)
+        self.assertEqual(code, 0)
+        self.assertIn(self.dump, [dump["path"] for dump in report["core_dumps"]])
+        self.assertIn(self.lost, [tree["path"] for tree in report["worktrees"]])
+        self.assertIsNotNone(report["docker"])
+
+    def test_cli_report_refuses_apply(self) -> None:
+        self.assertEqual(self._cli("--report", "--apply"), (2, ""))
+
+    def test_worktrees_and_orphaned_agent_dir(self) -> None:
+        trees = {t["path"]: t for t in self._report()["worktrees"]}
+
+        expected = {
+            self.clean,
+            self.kept,
+            self.lost,
+            self.detached,
+            self.agent,
+            self.orphan,
+        }
+        self.assertEqual(set(trees), expected)
+        self.assertTrue(trees[self.orphan]["orphaned"])
+        self.assertFalse(trees[self.agent]["orphaned"])
+        self.assertEqual(trees[self.kept]["branch"], "kept")
+        self.assertIsNone(trees[self.detached]["branch"])
+        for tree in trees.values():
+            self.assertGreater(tree["size_bytes"], 0)
+            self.assertIsNotNone(tree["last_activity"])
+            self.assertEqual(tree["foreign_entries"], 0)
+
+    def test_foreign_entries_through_patched_owner_check(self) -> None:
+        with patch.object(
+            walk_module,
+            "is_foreign",
+            side_effect=lambda path, st: os.path.basename(path) == "new.txt",
+        ):
+            trees = {t["path"]: t for t in self._report()["worktrees"]}
+
+        self.assertEqual(trees[self.lost]["foreign_entries"], 1)
+        self.assertEqual(trees[self.clean]["foreign_entries"], 0)
+
+    def test_preserved_verdicts_and_nothing_written(self) -> None:
+        before = git(self.kept, "status", "--porcelain=v2", "--untracked-files=all")
+
+        verdicts = {p["path"]: p for p in self._report()["preserved"]}
+
+        self.assertEqual(set(verdicts), {self.kept, self.lost, self.detached})
+        self.assertTrue(verdicts[self.kept]["preserved"])
+        self.assertEqual(verdicts[self.kept]["paths"], 2)
+        self.assertFalse(verdicts[self.lost]["preserved"])
+        self.assertEqual(verdicts[self.lost]["reasons"], ["new.txt: content in no ref"])
+        self.assertFalse(verdicts[self.detached]["preserved"])
+        self.assertEqual(
+            verdicts[self.detached]["reasons"], ["detached HEAD reachable from no ref"]
+        )
+        after = git(self.kept, "status", "--porcelain=v2", "--untracked-files=all")
+        self.assertEqual(before, after)
+
+    def test_roots_core_dumps_docker_and_balance(self) -> None:
+        report = self._report()
+
+        children = report["roots"][0]["children"]
+        self.assertEqual(
+            [(os.path.basename(c["path"]), c["kind"]) for c in children],
+            [("bigdir", "dir"), ("core", "core-dump"), ("core.12", "file")],
+        )
+        self.assertEqual([d["path"] for d in report["core_dumps"]], [self.dump])
+        dump = report["core_dumps"][0]
+        self.assertEqual(dump["apparent_bytes"], 1 << 30)
+        self.assertLess(dump["size_bytes"], dump["apparent_bytes"])
+        self.assertEqual(report["docker"][0]["total"], 3)
+        self.assertEqual(len(report["balance"]), 1)
+        listed = sum(c["size_bytes"] for c in children)
+        listed += sum(t["size_bytes"] for t in report["worktrees"])
+        self.assertEqual(report["balance"][0]["attributed_bytes"], listed)
+        self.assertEqual(report["warnings"], [])
+        json.dumps(report)
+        text = render_text(report)
+        self.assertIn("orphaned", text)
+        self.assertIn("core-dump", text)
+
+    def test_unknown_repo_and_root_are_warnings(self) -> None:
+        missing = os.path.join(self.tmp, "absent")
+
+        report = disk_report([missing], [self.root], THRESHOLD, docker=False)
+
+        self.assertEqual(report["worktrees"], [])
+        self.assertIsNone(report["docker"])
+        self.assertEqual(len(report["warnings"]), 2)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/__init__.py b/tests/unit/pkgmgr/actions/gc/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/unit/pkgmgr/actions/gc/report/__init__.py b/tests/unit/pkgmgr/actions/gc/report/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_balance.py b/tests/unit/pkgmgr/actions/gc/report/test_balance.py
new file mode 100644
index 0000000..08aa5aa
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_balance.py
@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+
+from pkgmgr.actions.gc.report.balance import balance
+
+
+class TestBalance(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp = tempfile.TemporaryDirectory()
+        self.root = os.path.realpath(self._tmp.name)
+        for rel in ("a/b", "c", "a-x"):
+            os.makedirs(os.path.join(self.root, rel))
+
+    def tearDown(self) -> None:
+        self._tmp.cleanup()
+
+    def _path(self, rel: str) -> str:
+        return os.path.join(self.root, rel)
+
+    def test_nested_and_repeated_items_count_once(self) -> None:
+        items = [
+            (self._path("a/b"), 50),
+            (self._path("a"), 100),
+            (self._path("a-x"), 7),
+            (self._path("c"), 10),
+            (self._path("c"), 10),
+            (self._path("gone"), 1000),
+        ]
+
+        rows = balance([self.root, self.root], items)
+
+        self.assertEqual(len(rows), 1)
+        row = rows[0]
+        self.assertEqual(row["attributed_bytes"], 117)
+        self.assertTrue(os.path.ismount(row["filesystem"]))
+        self.assertGreater(row["total_bytes"], 0)
+        self.assertLessEqual(row["free_bytes"], row["total_bytes"])
+
+    def test_unreadable_paths_get_no_row(self) -> None:
+        self.assertEqual(balance([self._path("gone")], []), [])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_core_dumps.py b/tests/unit/pkgmgr/actions/gc/report/test_core_dumps.py
new file mode 100644
index 0000000..0739dcd
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_core_dumps.py
@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+from unittest.mock import ANY, patch
+
+from pkgmgr.actions.gc.report.core_dumps import (
+    ELF_HEADER,
+    ET_CORE,
+    core_dumps,
+    is_core_dump,
+)
+
+ET_EXEC = 2
+
+
+def elf(e_type: int, order: str = "little") -> bytes:
+    data = 1 if order == "little" else 2
+    return b"\x7fELF" + bytes([2, data, 1]) + bytes(9) + e_type.to_bytes(2, order)
+
+
+class TestCoreDumps(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp = tempfile.TemporaryDirectory()
+        self.root = os.path.realpath(self._tmp.name)
+
+    def tearDown(self) -> None:
+        self._tmp.cleanup()
+
+    def _file(self, name: str, data: bytes, size: int | None = None) -> str:
+        path = os.path.join(self.root, name)
+        with open(path, "wb") as fh:
+            fh.write(data + bytes(46))
+        if size is not None:
+            os.truncate(path, size)
+        return path
+
+    def test_et_core_is_detected_in_both_byte_orders(self) -> None:
+        self.assertTrue(is_core_dump(self._file("core", elf(ET_CORE))))
+        self.assertTrue(is_core_dump(self._file("core.1", elf(ET_CORE, "big"))))
+
+    def test_other_elf_types_and_non_elf_are_ignored(self) -> None:
+        self.assertFalse(is_core_dump(self._file("core", elf(ET_EXEC))))
+        self.assertFalse(is_core_dump(self._file("core.2", b"#!/bin/sh\n")))
+        short = os.path.join(self.root, "core.3")
+        with open(short, "wb") as fh:
+            fh.write(b"\x7fELF")
+        self.assertFalse(is_core_dump(short))
+
+    def test_symlink_is_not_followed(self) -> None:
+        target = self._file("real", elf(ET_CORE))
+        link = os.path.join(self.root, "core")
+        os.symlink(target, link)
+
+        self.assertFalse(is_core_dump(link))
+
+    def test_reads_no_more_than_the_elf_header(self) -> None:
+        path = self._file("core", elf(ET_CORE), size=1 << 20)
+
+        with patch("os.read", wraps=os.read) as read:
+            is_core_dump(path)
+
+        read.assert_called_once_with(ANY, ELF_HEADER)
+
+    def test_sparse_dump_is_sized_by_blocks_and_others_dropped(self) -> None:
+        dump = self._file("core", elf(ET_CORE), size=1 << 30)
+        binary = self._file("core.7", elf(ET_EXEC))
+
+        dumps = core_dumps([dump, binary, dump])
+
+        self.assertEqual([d["path"] for d in dumps], [dump])
+        self.assertEqual(dumps[0]["apparent_bytes"], 1 << 30)
+        self.assertLess(dumps[0]["size_bytes"], dumps[0]["apparent_bytes"])
+        self.assertEqual(dumps[0]["mtime"], os.lstat(dump).st_mtime)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_docker_usage.py b/tests/unit/pkgmgr/actions/gc/report/test_docker_usage.py
new file mode 100644
index 0000000..8ab6e0f
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_docker_usage.py
@@ -0,0 +1,62 @@
+from __future__ import annotations
+
+import subprocess
+import unittest
+from unittest.mock import patch
+
+from pkgmgr.actions.gc.report import docker_usage as module
+
+DF_OUTPUT = (
+    '{"Active":"2","Reclaimable":"1.2GB (50%)","Size":"2.4GB",'
+    '"TotalCount":"10","Type":"Images"}\n'
+    '{"Active":"0","Reclaimable":"0B","Size":"0B","TotalCount":"0",'
+    '"Type":"Build Cache"}\n'
+)
+
+
+class TestDockerUsage(unittest.TestCase):
+    def test_rows_are_parsed_from_json_lines(self) -> None:
+        with patch.object(module, "_docker", return_value=DF_OUTPUT) as docker:
+            rows, warning = module.docker_usage()
+
+        docker.assert_called_once_with(["system", "df", "--format", "{{json .}}"])
+        self.assertIsNone(warning)
+        self.assertEqual(
+            rows[0],
+            {
+                "type": "Images",
+                "total": 10,
+                "active": 2,
+                "size": "2.4GB",
+                "reclaimable": "1.2GB (50%)",
+            },
+        )
+        self.assertEqual(rows[1]["type"], "Build Cache")
+
+    def test_missing_docker_is_a_warning(self) -> None:
+        with patch.object(module, "_docker", side_effect=FileNotFoundError):
+            rows, warning = module.docker_usage()
+
+        self.assertIsNone(rows)
+        self.assertIn("not installed", warning)
+
+    def test_failing_docker_is_a_warning(self) -> None:
+        error = subprocess.CalledProcessError(
+            1, ["docker", "system", "df"], stderr="daemon down"
+        )
+        with patch.object(module, "_docker", side_effect=error):
+            rows, warning = module.docker_usage()
+
+        self.assertIsNone(rows)
+        self.assertIn("daemon down", warning)
+
+    def test_unparsable_output_is_a_warning(self) -> None:
+        with patch.object(module, "_docker", return_value="TYPE TOTAL\n[1]\n"):
+            rows, warning = module.docker_usage()
+
+        self.assertIsNone(rows)
+        self.assertIn("not JSON lines", warning)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_preserved.py b/tests/unit/pkgmgr/actions/gc/report/test_preserved.py
new file mode 100644
index 0000000..2eb3e89
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_preserved.py
@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+from unittest.mock import patch
+
+from pkgmgr.actions.gc.report import preserved as module
+
+HEAD_BLOB = "1" * 40
+INDEX_BLOB = "2" * 40
+STATUS = "\0".join(
+    [
+        f"1 .M N... 100644 100644 100644 {HEAD_BLOB} {INDEX_BLOB} dir/a file.txt",
+        " ".join(
+            ["u UU N...", *["100644"] * 4, HEAD_BLOB, INDEX_BLOB, HEAD_BLOB, "c.txt"]
+        ),
+        "? new file",
+        "",
+    ]
+)
+
+
+class TestPreservedParsing(unittest.TestCase):
+    def test_status_records_keep_paths_with_spaces(self) -> None:
+        with patch.object(module, "_git", return_value=STATUS):
+            entries = module._status_entries("/wt")
+
+        self.assertEqual(
+            entries,
+            [
+                ("dir/a file.txt", INDEX_BLOB),
+                ("c.txt", module.UNMERGED),
+                ("new file", None),
+            ],
+        )
+
+    def test_blob_must_sit_at_the_same_path_of_some_tip(self) -> None:
+        wanted = [("a", {HEAD_BLOB}), ("b", {HEAD_BLOB, INDEX_BLOB})]
+        answer = f"{HEAD_BLOB}\nt2:a missing\n{HEAD_BLOB}\nt2:b missing"
+
+        with patch.object(module, "run", return_value=answer) as run:
+            absent = module._absent("/repo", ["t1", "t2"], wanted)
+
+        self.assertEqual(absent, ["b"])
+        self.assertEqual(run.call_args.kwargs["input_text"], "t1:a\nt2:a\nt1:b\nt2:b\n")
+
+    def test_special_files_are_never_opened(self) -> None:
+        with tempfile.TemporaryDirectory() as tree:
+            os.mkfifo(os.path.join(tree, "fifo"))
+            os.mkdir(os.path.join(tree, "sub"))
+
+            with patch.object(module, "run") as run:
+                hashes = module._hashes(tree, ["fifo", "gone", "sub"])
+
+        run.assert_not_called()
+        self.assertEqual(
+            hashes,
+            {"fifo": module.SPECIAL, "gone": module.DELETED, "sub": module.DIRECTORY},
+        )
+
+    def test_no_tips_means_nothing_is_preserved(self) -> None:
+        with patch.object(module, "run") as run:
+            self.assertEqual(module._absent("/repo", [], [("a", {HEAD_BLOB})]), ["a"])
+
+        run.assert_not_called()
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_render.py b/tests/unit/pkgmgr/actions/gc/report/test_render.py
new file mode 100644
index 0000000..b5da198
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_render.py
@@ -0,0 +1,123 @@
+from __future__ import annotations
+
+import unittest
+
+from pkgmgr.actions.gc.report.render import render_text
+
+NOW = 1_000_000.0
+
+
+def report(**overrides: object) -> dict:
+    base = {
+        "generated_at": NOW,
+        "threshold_bytes": 1 << 20,
+        "worktrees": [
+            {
+                "path": "/r/.worktrees/x",
+                "branch": None,
+                "orphaned": False,
+                "missing": False,
+                "size_bytes": 3 << 30,
+                "last_activity": NOW - 2 * 86400,
+                "foreign_entries": 4,
+            },
+            {
+                "path": "/r/.claude/worktrees/agent-1",
+                "branch": None,
+                "orphaned": True,
+                "missing": False,
+                "size_bytes": 5 << 20,
+                "last_activity": NOW - 90,
+                "foreign_entries": 0,
+            },
+        ],
+        "preserved": [
+            {
+                "path": "/r/.worktrees/x",
+                "branch": None,
+                "paths": 2,
+                "preserved": False,
+                "reasons": [
+                    "detached HEAD reachable from no ref",
+                    "a: content in no ref",
+                ],
+            }
+        ],
+        "roots": [
+            {
+                "root": "/tmp",
+                "children": [
+                    {
+                        "path": "/tmp/core",
+                        "kind": "core-dump",
+                        "size_bytes": 2 << 20,
+                        "newest_mtime": NOW - 3 * 3600,
+                    }
+                ],
+            }
+        ],
+        "core_dumps": [
+            {
+                "path": "/tmp/core",
+                "size_bytes": 2 << 20,
+                "apparent_bytes": 1 << 30,
+                "mtime": NOW - 3 * 3600,
+            }
+        ],
+        "docker": None,
+        "balance": [
+            {
+                "filesystem": "/",
+                "total_bytes": 100 << 30,
+                "free_bytes": 10 << 30,
+                "attributed_bytes": 3 << 30,
+            }
+        ],
+        "warnings": ["docker unavailable: not installed"],
+    }
+    return {**base, **overrides}
+
+
+class TestRenderText(unittest.TestCase):
+    def test_sections_and_rows(self) -> None:
+        lines = render_text(report()).splitlines()
+
+        self.assertIn("== worktrees", lines)
+        worktree = next(line for line in lines if line.endswith("/r/.worktrees/x"))
+        self.assertEqual(
+            worktree.split(),
+            ["3.0G", "2.0d", "4", "linked", "(detached)", "/r/.worktrees/x"],
+        )
+        orphan = next(line for line in lines if "agent-1" in line)
+        self.assertEqual(orphan.split()[1:5], ["1.5m", "0", "orphaned", "-"])
+        verdict = next(line for line in lines if line.startswith("no "))
+        self.assertIn(
+            "detached HEAD reachable from no ref; a: content in no ref", verdict
+        )
+        self.assertIn("== root /tmp (over 1.0M)", lines)
+        rows = [line.split() for line in lines]
+        self.assertIn(["2.0M", "1.0G", "3.0h", "/tmp/core"], rows)
+        self.assertIn(["/", "100.0G", "10.0G", "3.0G"], rows)
+        self.assertEqual(lines[-1], "WARN  docker unavailable: not installed")
+        self.assertNotIn("== docker", lines)
+
+    def test_docker_rows_and_empty_sections(self) -> None:
+        docker = [
+            {
+                "type": "Images",
+                "total": 3,
+                "active": 1,
+                "size": "1GB",
+                "reclaimable": "0B",
+            }
+        ]
+
+        text = render_text(report(docker=docker, core_dumps=[], warnings=[]))
+
+        self.assertIn("== core dumps\n(none)", text)
+        self.assertIn("== docker", text)
+        self.assertIn("Images  3      1       1GB   0B", text)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_roots.py b/tests/unit/pkgmgr/actions/gc/report/test_roots.py
new file mode 100644
index 0000000..1aaea04
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_roots.py
@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+
+from pkgmgr.actions.gc.report.roots import scan_root
+
+THRESHOLD = 16 * 1024
+ET_CORE_HEADER = b"\x7fELF\x02\x01\x01" + bytes(9) + (4).to_bytes(2, "little")
+
+
+class TestScanRoot(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp = tempfile.TemporaryDirectory()
+        self.root = os.path.realpath(self._tmp.name)
+
+    def tearDown(self) -> None:
+        self._tmp.cleanup()
+
+    def _write(self, rel: str, size: int = 0, head: bytes = b"") -> str:
+        path = os.path.join(self.root, rel)
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "wb") as fh:
+            fh.write(head + b"d" * size)
+        return path
+
+    def _big(self, rel: str, size: int = 64 * 1024) -> str:
+        return self._write(rel, size)
+
+    def test_children_over_threshold_get_kinds_biggest_first(self) -> None:
+        self._big("node_modules/pkg/index.js", 200 * 1024)
+        self._big("wt/data", 180 * 1024)
+        self._write("wt/.git", head=b"gitdir: /elsewhere\n")
+        self._big("clone/.git/objects/pack", 160 * 1024)
+        self._big("bare.git/objects/blob", 140 * 1024)
+        self._write("bare.git/HEAD", head=b"ref: refs/heads/main\n")
+        self._big("venv/lib/site.py", 120 * 1024)
+        self._write("venv/pyvenv.cfg", head=b"home = /usr\n")
+        self._big(".cache/blob", 100 * 1024)
+        self._big("tagged/blob", 90 * 1024)
+        self._write("tagged/CACHEDIR.TAG", head=b"Signature: x\n")
+        self._big("plain/blob", 80 * 1024)
+        self._write("core", 70 * 1024, head=ET_CORE_HEADER)
+        self._big("loose.bin", 60 * 1024)
+        self._write("small/file", 10)
+        cores: list[str] = []
+
+        scanned = scan_root(self.root, THRESHOLD, cores)
+
+        kinds = [(os.path.basename(c["path"]), c["kind"]) for c in scanned["children"]]
+        self.assertEqual(
+            kinds,
+            [
+                ("node_modules", "node_modules"),
+                ("wt", "worktree"),
+                ("clone", "git-repo"),
+                ("bare.git", "git-repo"),
+                ("venv", "venv"),
+                (".cache", "cache"),
+                ("tagged", "cache"),
+                ("plain", "dir"),
+                ("core", "core-dump"),
+                ("loose.bin", "file"),
+            ],
+        )
+        self.assertEqual(scanned["root"], self.root)
+        self.assertEqual(cores, [os.path.join(self.root, "core")])
+        sizes = [c["size_bytes"] for c in scanned["children"]]
+        self.assertEqual(sizes, sorted(sizes, reverse=True))
+        self.assertTrue(all(c["newest_mtime"] > 0 for c in scanned["children"]))
+
+    def test_missing_root_raises(self) -> None:
+        with self.assertRaises(OSError):
+            scan_root(os.path.join(self.root, "absent"), THRESHOLD, [])
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/actions/gc/report/test_walk.py b/tests/unit/pkgmgr/actions/gc/report/test_walk.py
new file mode 100644
index 0000000..cc4e037
--- /dev/null
+++ b/tests/unit/pkgmgr/actions/gc/report/test_walk.py
@@ -0,0 +1,113 @@
+from __future__ import annotations
+
+import os
+import tempfile
+import unittest
+from unittest.mock import patch
+
+from pkgmgr.actions.gc.report import walk as walk_module
+from pkgmgr.actions.gc.report.walk import BLOCK, walk
+
+
+def allocated(*paths: str) -> int:
+    return sum(os.lstat(path).st_blocks * BLOCK for path in paths)
+
+
+class TestWalk(unittest.TestCase):
+    def setUp(self) -> None:
+        self._tmp = tempfile.TemporaryDirectory()
+        self.root = os.path.realpath(self._tmp.name)
+
+    def tearDown(self) -> None:
+        self._tmp.cleanup()
+
+    def _write(self, rel: str, data: bytes = b"x") -> str:
+        path = os.path.join(self.root, rel)
+        os.makedirs(os.path.dirname(path), exist_ok=True)
+        with open(path, "wb") as fh:
+            fh.write(data)
+        return path
+
+    def test_sparse_file_counts_allocated_blocks_only(self) -> None:
+        path = self._write("sparse")
+        os.truncate(path, 1 << 30)
+
+        stats = walk(self.root)
+
+        self.assertEqual(stats.size_bytes, allocated(self.root, path))
+        self.assertLess(stats.size_bytes, 1 << 30)
+
+    def test_symlink_target_is_not_followed(self) -> None:
+        with tempfile.TemporaryDirectory() as outside:
+            target = os.path.join(outside, "big")
+            with open(target, "wb") as fh:
+                fh.write(b"y" * (1 << 20))
+            link = os.path.join(self.root, "link")
+            os.symlink(target, link)
+
+            stats = walk(self.root)
+
+        self.assertEqual(stats.size_bytes, allocated(self.root, link))
+        self.assertLess(stats.size_bytes, 1 << 20)
+
+    def test_hard_link_is_counted_once(self) -> None:
+        first = self._write("a", b"z" * 65536)
+        os.link(first, os.path.join(self.root, "b"))
+
+        self.assertEqual(walk(self.root).size_bytes, allocated(self.root, first))
+
+    def test_foreign_entries_are_pruned_below_the_first_foreign_one(self) -> None:
+        self._write("foreign_dir/one")
+        self._write("foreign_dir/sub/two")
+        self._write("foreign_file")
+        self._write("mine")
+        plain = walk(self.root)
+
+        with patch.object(
+            walk_module,
+            "is_foreign",
+            side_effect=lambda path, st: os.path.relpath(path, self.root).startswith(
+                "foreign"
+            ),
+        ):
+            stats = walk(self.root)
+
+        self.assertEqual(plain.foreign_entries, 0)
+        self.assertEqual(stats.foreign_entries, 2)
+        self.assertEqual(stats.size_bytes, plain.size_bytes)
+
+    def test_files_named_like_core_dumps_are_candidates(self) -> None:
+        expected = {self._write("core"), self._write("deep/core.123")}
+        self._write("core.abc")
+        self._write("not-core")
+        os.makedirs(os.path.join(self.root, "dir", "core"))
+
+        self.assertEqual(set(walk(self.root).cores), expected)
+
+    @unittest.skipIf(os.getuid() == 0, "root lists every directory")
+    def test_unlistable_directory_is_counted(self) -> None:
+        locked = os.path.join(self.root, "locked")
+        os.mkdir(locked)
+        os.chmod(locked, 0)
+        try:
+            stats = walk(self.root)
+        finally:
+            os.chmod(locked, 0o700)
+
+        self.assertEqual(stats.unreadable, 1)
+
+    def test_missing_path_reports_unreadable(self) -> None:
+        stats = walk(os.path.join(self.root, "absent"))
+
+        self.assertEqual((stats.size_bytes, stats.unreadable), (0, 1))
+
+    def test_other_filesystem_is_skipped(self) -> None:
+        self._write("file")
+
+        stats = walk(self.root, dev=os.lstat(self.root).st_dev + 1)
+
+        self.assertEqual(stats.size_bytes, 0)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/tests/unit/pkgmgr/core/git/test_run.py b/tests/unit/pkgmgr/core/git/test_run.py
index efd365c..a10ea6e 100644
--- a/tests/unit/pkgmgr/core/git/test_run.py
+++ b/tests/unit/pkgmgr/core/git/test_run.py
@@ -40,6 +40,21 @@ class TestGitRun(unittest.TestCase):
         self.assertTrue(kwargs["text"])
         self.assertTrue(kwargs["capture_output"])
 
+    def test_scan_input_text_replaces_closed_stdin(self) -> None:
+        completed = MagicMock()
+        completed.stdout = "abc\n"
+
+        with patch(
+            "pkgmgr.core.git.run.subprocess.run", return_value=completed
+        ) as mock_run:
+            out = run(["cat-file", "--batch-check"], scan=True, input_text="x\n")
+
+        self.assertEqual(out, "abc")
+        kwargs = mock_run.call_args.kwargs
+        self.assertEqual(kwargs["input"], "x\n")
+        self.assertNotIn("stdin", kwargs)
+        self.assertIn("timeout", kwargs)
+
     def test_failure_raises_giterror_with_details(self) -> None:
         # Build a CalledProcessError with stdout/stderr populated
         import subprocess as sp