fix: fail closed when no safe export destination exists; polish salvage edges

- _profile_export_directory(): when the managed store, the home-sibling
  store, AND the temp dir all resolve inside Git checkouts, raise a clear
  ValueError instead of warning and proceeding — a stderr warning would not
  stop a scripted export from staging a secret-bearing archive in a source
  tree, which is the exact #92457 incident class. All three callers already
  surface ValueError cleanly (CLI/TUI print Error: + exit, API returns 400).
- .dockerignore: drop the /default.tar.gz line made redundant by the global
  *.tar.gz pattern this PR adds.
- hermes profile export -o help text: stop advertising the old
  <name>.tar.gz cwd default.
- Tests: cwd-in-unrelated-checkout topology (the second production shape
  from the blocking review) and the fail-closed path. Mutation-checked:
  both fail on the pre-fix helper.

.dockerignore

@@ -111,6 +111,5 @@ plans/
 /log.txt
 /sqlite_leak_fix.png
 /*.png.bak
-/default.tar.gz
 *.tar.gz
 *.tgz

hermes_cli/profiles.py

@@ -2154,13 +2154,14 @@ def _profile_export_directory() -> Path:
     for candidate in candidates:
         if not _inside_git_checkout(candidate):
             return candidate
-    logger.warning(
-        "Every managed export destination resolves inside a Git checkout; "
-        "falling back to %s. Pass an explicit output path to avoid staging "
-        "profile archives in a source tree.",
-        export_dir,
+    # Fail closed: writing a secret-bearing archive into a source tree is the
+    # incident this helper exists to prevent (#92457). A warning on stderr
+    # would not stop a scripted export from recreating it.
+    raise ValueError(
+        "No safe automatic export destination: every candidate directory is "
+        "inside a Git checkout. Pass an explicit output path outside the "
+        "checkout (e.g. -o /path/outside/repo/profile.tar.gz)."
     )
-    return export_dir
 
 
 def get_profile_export_path(name: str, *, timestamp: Optional[str] = None) -> Path:

hermes_cli/subcommands/profile.py

@@ -135,7 +135,9 @@ def build_profile_parser(subparsers, *, cmd_profile: Callable) -> None:
     )
     profile_export.add_argument("profile_name", help="Profile to export")
     profile_export.add_argument(
-        "-o", "--output", default=None, help="Output file (default: <name>.tar.gz)"
+        "-o", "--output", default=None,
+        help="Output file (default: a managed profile-exports/<name>-<timestamp>.tar.gz "
+             "under the default Hermes home)",
     )
 
     profile_import = profile_subparsers.add_parser(

tests/hermes_cli/test_profile_export_default_path.py

@@ -172,3 +172,43 @@ async def test_profile_export_api_uses_the_shared_managed_destination(
     result = await router_mod.export_profile_endpoint("default", ProfileExport())
 
     assert result == {"ok": True, "archive": str(managed)}
+
+
+def test_cwd_in_unrelated_checkout_does_not_prove_safety(
+    tmp_path, monkeypatch, profiles
+):
+    """cwd inside unrelated checkout A must not stand in for the safety proof
+    of a HERMES_HOME inside checkout B."""
+    checkout_b = tmp_path / "checkout-b"
+    checkout_b.mkdir()
+    (checkout_b / ".git").mkdir()
+    checkout_a = tmp_path / "checkout-a"
+    checkout_a.mkdir()
+    (checkout_a / ".git").write_text("gitdir: ../git\n", encoding="utf-8")
+    monkeypatch.chdir(checkout_a)
+    monkeypatch.setattr(Path, "home", lambda: tmp_path / "home")
+    monkeypatch.setattr(profiles, "_get_default_hermes_home", lambda: checkout_b)
+
+    result = profiles.get_profile_export_path("default", timestamp="20260823-120000")
+
+    assert not result.resolve().is_relative_to(checkout_b.resolve())
+    assert not result.resolve().is_relative_to(checkout_a.resolve())
+
+
+def test_every_candidate_inside_a_checkout_fails_closed(
+    tmp_path, monkeypatch, profiles
+):
+    """When home, sibling store, and tempdir all resolve inside checkouts the
+    helper must refuse — a warning would not stop a scripted export from
+    recreating the #92457 incident artifact."""
+    import tempfile
+
+    checkout = tmp_path / "checkout"
+    checkout.mkdir()
+    (checkout / ".git").mkdir()
+    monkeypatch.setattr(Path, "home", lambda: checkout / "home")
+    monkeypatch.setattr(profiles, "_get_default_hermes_home", lambda: checkout)
+    monkeypatch.setattr(tempfile, "gettempdir", lambda: str(checkout / "tmp"))
+
+    with pytest.raises(ValueError, match="No safe automatic export destination"):
+        profiles.get_profile_export_path("default")