WARDEN-WP-0026 T02: safe access transports (no secret values on stdout)

- proxy.py: proxy_fetch_to_file (mode-0600 file), build_wrapped_fetch +
  proxy_fetch_wrapped (single-use OpenBao response-wrapping token), _capture_value
  helper, is_bao_kv_fetch.
- warden access: --out FILE, --wrap [--wrap-ttl], --unsafe-stdout. Raw --fetch to a
  non-TTY stdout is refused (exit 6) — captured/piped output is the disclosure risk;
  sanctioned transports are --out / --exec / --wrap.
- canon: anti-pattern (secret value onto captured stdout) + transport table in
  .claude/rules/credential-routing.md; OperatorAccessAssist.md examples + G2 updated.
- tests: file/wrap/build + stdout-guard in tests/test_proxy.py. 293 pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/rules/credential-routing.md

@@ -39,6 +39,22 @@ Requires the `warden` CLI from `~/ops-warden` (`uv tool install .` or `uv run wa
 - `POST /messages/` to `ops-warden` asking for `ISSUE_CORE_API_KEY`, `OPENROUTER_API_KEY`, etc.
 - Inventing `warden secret`, `warden login`, `warden bao`, `warden tunnel` — they do not exist
 - Pasting secrets into Git, State Hub, workplans, logs, or chat
+- **Reading a secret value onto a captured stdout.** `bao kv get <path>` (full table)
+  or `bao kv get -field=X` piped/redirected/run in an agent session dumps the value
+  into a logged context — the 2026-07-16 disclosure. To *verify* a lane use
+  `bao token capabilities` (allow/deny), never a read (WP-0026 T01).
+
+### Safe fetch transports (WP-0026 T02)
+
+When a value must actually move, use a sanctioned transport that keeps it off
+stdout. `warden access <need> --fetch` refuses to stream a value to a non-terminal
+stdout unless you pass `--unsafe-stdout` (interactive human sessions only):
+
+| Transport | Command | Result |
+| --- | --- | --- |
+| **File** | `warden access <need> --out FILE` | value written to a mode-0600 file, never shown |
+| **Env (exec)** | `warden access <need> --exec -- <cmd>` | value injected into the child process env only |
+| **Wrapping token** | `warden access <need> --wrap` | a single-use, short-TTL OpenBao wrapping token to `bao unwrap` in your own context |
 
 ### Other capabilities (reuse-surface)
 

src/warden/cli.py

@@ -956,6 +956,10 @@ def _access_proxy(
     do_exec: bool,
     child_argv: list,
     no_policy: bool,
+    out_path: Optional[str] = None,
+    wrap: bool = False,
+    wrap_ttl: str = "5m",
+    unsafe_stdout: bool = False,
 ) -> None:
     """Proxy a non-SSH credential fetch as the caller (WP-0014 T3).
 
@@ -965,9 +969,12 @@ def _access_proxy(
     """
     from warden.proxy import (
         ProxyError,
+        build_wrapped_fetch,
         caller_auth_present,
         proxy_exec,
         proxy_fetch,
+        proxy_fetch_to_file,
+        proxy_fetch_wrapped,
         resolve_fetch_command,
         write_audit,
     )
@@ -1035,11 +1042,38 @@ def _access_proxy(
         else:
             err.print("[yellow]Proxying ungated[/yellow] (--no-policy; gate not enforced).")
 
-    try:
+    # Wrapping (WP-0026 T02) uses its own command shape; the value-bearing transports
-        resolved = resolve_fetch_command(entry, domain=domain, field=field, path=path)
+    # share the resolved fetch command.
-    except ProxyError as e:
+    if wrap and not is_login:
-        err.print(f"[red]{e}[/red]")
+        try:
-        raise typer.Exit(2)
+            resolved = build_wrapped_fetch(entry, path=path, ttl=wrap_ttl)
+        except ProxyError as e:
+            err.print(f"[red]{e}[/red]")
+            raise typer.Exit(2)
+    else:
+        try:
+            resolved = resolve_fetch_command(entry, domain=domain, field=field, path=path)
+        except ProxyError as e:
+            err.print(f"[red]{e}[/red]")
+            raise typer.Exit(2)
+
+    # T02 — the sanctioned fetch transports (file / env / wrapping token) never put a
+    # secret value on stdout. Streaming a value to stdout is the documented anti-pattern:
+    # allowed only to an interactive terminal, and only with an explicit acknowledgment
+    # when stdout is captured/piped (the logged-context disclosure risk).
+    if not is_login and not do_exec and not wrap and not out_path:
+        import sys as _sys
+
+        if not _sys.stdout.isatty() and not unsafe_stdout:
+            err.print(
+                "[red]Refusing to stream a secret value to a non-terminal stdout[/red] "
+                "(captured/piped output is a disclosure risk). Use a sanctioned transport:\n"
+                "  --out FILE     write the value to a mode-0600 file\n"
+                "  --exec -- CMD  inject it into a child process env\n"
+                "  --wrap         return a single-use OpenBao wrapping token to unwrap yourself\n"
+                "Override only for an interactive human session: --unsafe-stdout."
+            )
+            raise typer.Exit(6)
 
     action = "login" if is_login else ("exec" if do_exec else "fetch")
     err.print(
@@ -1052,6 +1086,18 @@ def _access_proxy(
                 err.print("[red]--exec needs a command after `--`[/red], e.g. `-- npm publish`.")
                 raise typer.Exit(2)
             rc = proxy_exec(resolved, env_var=field or "", child_argv=child_argv)
+        elif wrap:
+            token = proxy_fetch_wrapped(resolved)
+            # The wrapping token is not the secret value — safe to hand back on stdout.
+            print(token)
+            err.print(
+                f"[dim]wrapping token (single-use, ttl {wrap_ttl}) — unwrap in your own "
+                f"context: [bold]bao unwrap {'<token>'}[/bold][/dim]"
+            )
+            rc = 0
+        elif out_path:
+            rc = proxy_fetch_to_file(resolved, Path(out_path))
+            err.print(f"[dim]value written to {out_path} (mode 0600); not shown[/dim]")
         else:
             rc = proxy_fetch(resolved)
     except ProxyError as e:
@@ -1087,7 +1133,7 @@ def access(
     output_json: Annotated[bool, typer.Option("--json", help="Output JSON (stable, secret-free)")] = False,
     all_entries: Annotated[bool, typer.Option("--all", help="Include draft entries")] = False,
     do_fetch: Annotated[
-        bool, typer.Option("--fetch", help="Proxy the fetch as the caller; value streams to stdout")
+        bool, typer.Option("--fetch", help="Proxy the fetch as the caller (pair with --out/--wrap; raw stdout is guarded)")
     ] = False,
     do_exec: Annotated[
         bool,
@@ -1099,6 +1145,21 @@ def access(
     path: Annotated[
         Optional[str], typer.Option("--path", help="Override the owner-side path template")
     ] = None,
+    out_path: Annotated[
+        Optional[str],
+        typer.Option("--out", help="Sanctioned transport: write the value to this mode-0600 file, not stdout"),
+    ] = None,
+    wrap: Annotated[
+        bool,
+        typer.Option("--wrap", help="Sanctioned transport: return a single-use OpenBao wrapping token (bao unwrap)"),
+    ] = False,
+    wrap_ttl: Annotated[
+        str, typer.Option("--wrap-ttl", help="TTL for the --wrap response-wrapping token")
+    ] = "5m",
+    unsafe_stdout: Annotated[
+        bool,
+        typer.Option("--unsafe-stdout", help="Acknowledge streaming a value to a captured/piped stdout (anti-pattern)"),
+    ] = False,
     no_policy: Annotated[
         bool,
         typer.Option("--no-policy", help="Acknowledge proxying when the flex-auth gate is not enforced"),
@@ -1134,7 +1195,7 @@ def access(
 
     entry = matches[0]
 
-    if do_fetch or do_exec:
+    if do_fetch or do_exec or out_path or wrap:
         _access_proxy(
             entry,
             domain=domain,
@@ -1143,6 +1204,10 @@ def access(
             do_exec=do_exec,
             child_argv=list(ctx.args),
             no_policy=no_policy,
+            out_path=out_path,
+            wrap=wrap,
+            wrap_ttl=wrap_ttl,
+            unsafe_stdout=unsafe_stdout,
         )
         return
 

src/warden/proxy.py

@@ -205,6 +205,102 @@ def proxy_fetch(resolved: ResolvedFetch) -> int:
     return completed.returncode
 
 
+def _capture_value(resolved: ResolvedFetch) -> str:
+    """Run the fetch and return its stdout (the value) minus one trailing newline.
+
+    The value transits warden's memory (the accepted proxy tradeoff for the
+    non-stdout transports) but is never written to disk or log by this function.
+    """
+    env = _caller_env()
+    if resolved.argv is not None:
+        fetched = subprocess.run(  # noqa: S603
+            resolved.argv, stdout=subprocess.PIPE, stderr=None, stdin=None,
+            env=env, check=False, text=True,
+        )
+    else:
+        fetched = subprocess.run(  # noqa: S602
+            resolved.shell_cmd, shell=True, stdout=subprocess.PIPE, stderr=None,
+            stdin=None, env=env, check=False, text=True,
+        )
+    if fetched.returncode != 0:
+        raise ProxyError(
+            f"fetch failed (exit {fetched.returncode}) — check caller auth and the path."
+        )
+    value = fetched.stdout
+    if value.endswith("\n"):
+        value = value[:-1]
+    return value
+
+
+def proxy_fetch_to_file(resolved: ResolvedFetch, out_path: Path) -> int:
+    """Fetch the value and write it to ``out_path`` at mode 0600 — never to stdout.
+
+    A sanctioned transport (WP-0026 T02): the value goes to a private file the
+    caller controls, not a terminal or a logged stream. The file is created with
+    O_EXCL semantics widened to truncate-if-owned so a re-fetch overwrites, but the
+    mode is forced to 0600 before any bytes are written.
+    """
+    value = _capture_value(resolved)
+    # Open with restrictive mode from the start; do not echo the value anywhere.
+    fd = os.open(str(out_path), os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
+    try:
+        os.chmod(out_path, 0o600)  # enforce even if the file pre-existed with looser mode
+        with os.fdopen(fd, "w") as fh:
+            fh.write(value)
+    finally:
+        value = ""  # noqa: F841 — best-effort scrub of the local reference
+    return 0
+
+
+def is_bao_kv_fetch(entry: RouteEntry) -> bool:
+    """True when a lane's fetch is a plain ``bao kv get`` (wrappable, WP-0026 T02)."""
+    return bool(entry.fetch_command and entry.fetch_command.strip().startswith("bao kv get"))
+
+
+def build_wrapped_fetch(
+    entry: RouteEntry, *, path: Optional[str] = None, ttl: str = "5m"
+) -> ResolvedFetch:
+    """Build a response-wrapping fetch: ``bao kv get -wrap-ttl=<ttl> -format=json <path>``.
+
+    Response wrapping returns a single-use, short-TTL *wrapping token* instead of the
+    secret value — the sanctioned way to move a value between processes (WP-0026 T02).
+    The caller unwraps it in their own context (`bao unwrap`). Only valid for plain
+    ``bao kv get`` lanes; the whole secret is wrapped (a per-field ``-field`` read
+    cannot be wrapped).
+    """
+    if not is_bao_kv_fetch(entry):
+        raise ProxyError(
+            f"{entry.id!r} is not a plain `bao kv get` lane — response wrapping "
+            "(--wrap) is unavailable. Use --out FILE or --exec instead."
+        )
+    target = path or entry.path_template
+    if not target or _PLACEHOLDER.search(target):
+        raise ProxyError(
+            "--wrap needs a concrete path — supply --path or a resolved path_template."
+        )
+    return ResolvedFetch(argv=["bao", "kv", "get", f"-wrap-ttl={ttl}", "-format=json", target])
+
+
+def proxy_fetch_wrapped(resolved: ResolvedFetch) -> str:
+    """Run a wrapping fetch and return the wrapping *token* (not the secret value).
+
+    The token is single-use and short-lived; it is not itself the credential, so it
+    is safe to hand back on stdout. Parses OpenBao's ``-format=json`` wrap_info.
+    """
+    raw = _capture_value(resolved)
+    try:
+        data = json.loads(raw)
+        token = data["wrap_info"]["token"]
+    except (json.JSONDecodeError, KeyError, TypeError) as e:
+        raise ProxyError(
+            "could not parse a wrapping token from the fetch output "
+            "(is response wrapping supported for this path?)."
+        ) from e
+    if not token:
+        raise ProxyError("empty wrapping token returned.")
+    return str(token)
+
+
 def proxy_exec(resolved: ResolvedFetch, *, env_var: str, child_argv: List[str]) -> int:
     """Fetch the value and inject it into a child command's environment only.
 

tests/test_proxy.py

@@ -287,3 +287,80 @@ def test_invalid_lane_rejected(tmp_path):
     import pytest
     with pytest.raises(CatalogError, match="invalid lane"):
         load_catalog(p)
+
+
+# ---------------------------------------------------------------------------
+# Safe access transports (WARDEN-WP-0026 T02) — no secret values on stdout
+# ---------------------------------------------------------------------------
+
+from warden.proxy import (  # noqa: E402
+    build_wrapped_fetch,
+    is_bao_kv_fetch,
+    proxy_fetch_to_file,
+    proxy_fetch_wrapped,
+)
+
+
+def test_fetch_to_file_writes_mode_0600_and_no_stdout(tmp_path, capsys):
+    out = tmp_path / "secret.out"
+    rc = proxy_fetch_to_file(ResolvedFetch(shell_cmd="printf 'sekret'"), out)
+    assert rc == 0
+    assert out.read_text() == "sekret"
+    assert oct(out.stat().st_mode & 0o777) == "0o600"
+    # nothing printed to stdout/stderr by the transport itself
+    captured = capsys.readouterr()
+    assert "sekret" not in captured.out and "sekret" not in captured.err
+
+
+def test_fetch_to_file_forces_0600_on_preexisting_loose_file(tmp_path):
+    out = tmp_path / "pre.out"
+    out.write_text("old")
+    out.chmod(0o644)
+    proxy_fetch_to_file(ResolvedFetch(shell_cmd="printf 'new'"), out)
+    assert out.read_text() == "new"
+    assert oct(out.stat().st_mode & 0o777) == "0o600"
+
+
+def test_wrapped_fetch_returns_token_not_value():
+    payload = '{"wrap_info":{"token":"hvs.WRAP"}}'
+    token = proxy_fetch_wrapped(ResolvedFetch(shell_cmd=f"printf '%s' '{payload}'"))
+    assert token == "hvs.WRAP"
+
+
+def test_wrapped_fetch_bad_output_raises():
+    with pytest.raises(ProxyError, match="wrapping token"):
+        proxy_fetch_wrapped(ResolvedFetch(shell_cmd="printf 'not-json'"))
+
+
+def test_build_wrapped_fetch_only_for_bao_kv():
+    bao = _entry(fetch_command="bao kv get -field=API_TOKEN platform/x", path_template="platform/x")
+    assert is_bao_kv_fetch(bao)
+    argv = build_wrapped_fetch(bao, ttl="9m").argv
+    assert argv == ["bao", "kv", "get", "-wrap-ttl=9m", "-format=json", "platform/x"]
+
+    piped = _entry(fetch_command="kubectl get secret x -o json | base64 -d", path_template="x")
+    assert not is_bao_kv_fetch(piped)
+    with pytest.raises(ProxyError, match="response wrapping"):
+        build_wrapped_fetch(piped)
+
+
+def test_build_wrapped_fetch_refuses_placeholder_path():
+    e = _entry(fetch_command="bao kv get -field=<FIELD> <path_template>",
+               path_template="platform/workloads/<domain>/x")
+    with pytest.raises(ProxyError, match="concrete path"):
+        build_wrapped_fetch(e)
+
+
+def test_access_fetch_to_nonterminal_stdout_is_refused(tmp_path, monkeypatch):
+    """The anti-pattern: streaming a value to captured stdout is refused (exit 6)."""
+    _proxy_env(monkeypatch, tmp_path)
+    monkeypatch.setenv("VAULT_TOKEN", "caller-token")  # G1 caller-auth precheck
+    # The guard trips before the fetch runs; make a real bao call fail loudly if reached.
+    monkeypatch.setattr(
+        "warden.proxy.subprocess.run",
+        lambda *a, **k: (_ for _ in ()).throw(AssertionError("fetch ran despite stdout guard")),
+    )
+    # CliRunner captures stdout (not a tty), so the guard trips without --unsafe-stdout.
+    r = runner.invoke(app, ["access", "whynot-design-npm-publish", "--fetch", "--no-policy"])
+    assert r.exit_code == 6
+    assert "sanctioned transport" in r.output.lower() or "refusing" in r.output.lower()

wiki/OperatorAccessAssist.md

@@ -22,14 +22,21 @@ audited"). It does **not** move secret custody into ops-warden.
 ```console
 # advisory — works with no config; never fetches a value
 $ warden access "npm token" --domain coulomb_social
-# proxy a secret read as the caller (gated + audited); value streams to stdout
+# --- sanctioned transports (WP-0026 T02): value never hits stdout ---
-$ warden access "npm token" --domain coulomb_social --field NPM_AUTH_TOKEN --path <p> --fetch
+# write the value to a mode-0600 file
+$ warden access "npm token" --domain coulomb_social --field NPM_AUTH_TOKEN --path <p> --fetch --out ./npm.token
 # run a child command with the secret in its env only (à la `op run`)
 $ warden access "npm token" --field NPM_AUTH_TOKEN --exec -- npm publish
+# return a single-use OpenBao wrapping token to unwrap in your own context
+$ warden access "npm token" --path <p> --wrap        # then: bao unwrap <token>
 # interactive login (login lane): no token required, no secret-read gate
 $ warden access "login oidc" --domain coulomb_social --fetch
 ```
 
+> **Raw `--fetch` to stdout is the anti-pattern.** It is refused when stdout is
+> captured or piped (a logged-context disclosure risk); pass `--unsafe-stdout` only
+> for an interactive human terminal. Prefer `--out` / `--exec` / `--wrap`.
+
 `--json` gives a stable, secret-free shape for agentic operators.
 
 ---
@@ -60,7 +67,7 @@ prevent, and duplicates OpenBao.
 | | Guardrail | How it is enforced |
 | --- | --- | --- |
 | **G1** | **Caller identity, never warden's** | The proxy runs the owner's tool with the caller's own environment; ops-warden injects no token of its own. Secret lanes require the caller to already hold a credential (`caller_auth_present`), else they fail with the auth pointer. |
-| **G2** | **Transit only — no persistence/logging of values** | `--fetch` runs with **inherited stdout** (never a pipe), so the value streams to the caller and never enters warden's memory. `--exec` reads the value solely to place it in a child process's env (the accepted `--exec` tradeoff) — never to disk or log. The audit record is **metadata only**. |
+| **G2** | **Transit only — no persistence/logging of values** | Sanctioned transports keep the value off stdout: `--out` writes it to a mode-0600 file, `--exec` injects it into a child process env, `--wrap` returns a single-use OpenBao wrapping token (not the value). Raw `--fetch` to stdout is refused for captured/piped output (`--unsafe-stdout` overrides for a human terminal). warden never writes the value to disk or log; the audit record is **metadata only**. (WP-0026 T02) |
 | **G3** | **Policy gate before fetch** | `check_fetch_policy` (flex-auth) runs before any secret-lane fetch. With `policy.enabled: false` the proxy refuses unless `--no-policy` is given to acknowledge proxying ungated. |
 
 The catalog side enforces a fourth, upstream guard: **handoff fields are templates,

workplans/WARDEN-WP-0026-credential-disclosure-hygiene.md

@@ -88,11 +88,20 @@ it (see T07).
 
 ```task
 id: WARDEN-WP-0026-T02
-status: todo
+status: done
 priority: high
 state_hub_task_id: "3f28c573-8e58-4851-8aa0-925f9367f266"
 ```
 
+Done 2026-07-16: sanctioned transports added to `warden access` so a value never
+lands on stdout — `--out FILE` (mode-0600 file), `--exec` (child env, pre-existing),
+and `--wrap` (single-use OpenBao response-wrapping token via `bao kv get -wrap-ttl`,
+caller `bao unwrap`s in their own context). Raw `--fetch` to a non-TTY stdout is now
+refused (exit 6) unless `--unsafe-stdout` is passed (interactive human only).
+`proxy_fetch_to_file`/`proxy_fetch_wrapped`/`build_wrapped_fetch` in `proxy.py`; tests
+in `tests/test_proxy.py`. Anti-pattern + transports documented fleet-wide in
+`.claude/rules/credential-routing.md` and `wiki/OperatorAccessAssist.md` (G2).
+
 `warden access` / fetch paths must emit values only into an env var, a file, or
 a **response-wrapping token** (`bao … -wrap-ttl`), never a stdout table. Add a
 wrapping-token transport for values that must move between processes. Record in