fix: harden structured auth MCP errors against reviewer findings (#699)

Address PR #701 request-changes-class defects:

1. Fixed messages only — never embed HTTP bodies, Keychain, or exception
   text in tool results or daemon logs; sanitization fails closed.
2. Narrow Tool.run boundary wraps original success path; re-raises
   UrlElicitationRequiredError; install is idempotent.
3. No RuntimeError substring heuristics; only typed client failures
   are classified as auth/authz/network/config.
4. Central classify_http_status — every HTTP 403 is GiteaAuthzError.

Regressions cover adversarial secrets, stdio survival, elicitation,
parser RuntimeError, generic 403, repeated install, profiles, provenance.

Closes #699

gitea_auth.py

@@ -243,6 +243,192 @@ def _redact(text):
         return str(text)
 
 
+# ── Classified client failures (#699) ─────────────────────────────────────────
+# Subclasses of RuntimeError preserve existing ``except RuntimeError`` call
+# sites. Exception *messages* are fixed constants only — HTTP response bodies,
+# Keychain material, and arbitrary exception text are never stored on the
+# exception or re-emitted to tool results / daemon logs.
+
+
+# Fixed messages (must match mcp_tool_error_boundary.FIXED_MESSAGES keys used here).
+_MSG_AUTH_INVALID = "Gitea authentication failed: invalid or revoked credentials"
+_MSG_AUTH_FAILED = "Gitea authentication failed"
+_MSG_AUTHZ_SCOPE = "Gitea authorization failed: insufficient token scope"
+_MSG_AUTHZ_DENIED = "Gitea authorization failed: access denied"
+_MSG_NETWORK = "Network error contacting Gitea"
+_MSG_CONFIG = "Gitea configuration or credential resolution failed"
+_MSG_UPSTREAM = "Gitea upstream unavailable"
+_MSG_HTTP = "Gitea HTTP request failed"
+
+
+class GiteaClientError(RuntimeError):
+    """Base for known Gitea client failures with stable reason_code metadata."""
+
+    reason_code = "client_error"
+    error_class = "client"
+    http_status = None
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        if reason_code is not None:
+            self.reason_code = reason_code
+        if http_status is not None:
+            self.http_status = http_status
+        # Message is always a fixed constant; callers cannot inject bodies.
+        fixed = message if message is not None else _MSG_HTTP
+        super().__init__(fixed)
+
+
+class GiteaAuthError(GiteaClientError):
+    """Authentication failure (invalid/revoked credentials → typically HTTP 401)."""
+
+    reason_code = "auth_invalid_token"
+    error_class = "authentication"
+    http_status = 401
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        super().__init__(
+            message if message is not None else _MSG_AUTH_INVALID,
+            reason_code=reason_code or "auth_invalid_token",
+            http_status=http_status if http_status is not None else 401,
+        )
+
+
+class GiteaAuthzError(GiteaClientError):
+    """Authorization failure (HTTP 403 — scope deficiency or access denied)."""
+
+    reason_code = "authz_denied"
+    error_class = "authorization"
+    http_status = 403
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        code = reason_code or "authz_denied"
+        if code == "authz_insufficient_scope":
+            fixed = _MSG_AUTHZ_SCOPE
+        else:
+            fixed = _MSG_AUTHZ_DENIED
+            code = "authz_denied"
+        super().__init__(
+            message if message is not None else fixed,
+            reason_code=code,
+            http_status=http_status if http_status is not None else 403,
+        )
+
+
+class GiteaNetworkError(GiteaClientError):
+    """Transport / DNS / timeout failure contacting Gitea."""
+
+    reason_code = "network_error"
+    error_class = "network"
+    http_status = None
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        super().__init__(
+            message if message is not None else _MSG_NETWORK,
+            reason_code=reason_code or "network_error",
+            http_status=http_status,
+        )
+
+
+class GiteaConfigError(GiteaClientError):
+    """Local configuration / credential resolution failure (not HTTP auth)."""
+
+    reason_code = "config_error"
+    error_class = "configuration"
+    http_status = None
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        super().__init__(
+            message if message is not None else _MSG_CONFIG,
+            reason_code=reason_code or "config_error",
+            http_status=http_status,
+        )
+
+
+class GiteaHttpError(GiteaClientError):
+    """Non-auth HTTP failure with fixed message (no response body)."""
+
+    reason_code = "http_error"
+    error_class = "client"
+    http_status = None
+
+    def __init__(self, message=None, *, reason_code=None, http_status=None):
+        code = reason_code or "http_error"
+        if code == "upstream_unavailable":
+            fixed = _MSG_UPSTREAM
+        else:
+            fixed = _MSG_HTTP
+            code = "http_error"
+        super().__init__(
+            message if message is not None else fixed,
+            reason_code=code,
+            http_status=http_status,
+        )
+
+
+def _looks_like_insufficient_scope(detail: str) -> bool:
+    """Internal: inspect redacted body *only* to refine 403 reason_code.
+
+    The body is never stored on the exception or returned to callers.
+    """
+    lower = (detail or "").lower()
+    markers = (
+        "insufficient scope",
+        "required scope",
+        "does not have at least one of required scope",
+        "token does not have",
+        "missing scope",
+        "scope(s)",
+    )
+    return any(m in lower for m in markers)
+
+
+def classify_http_status(code: int, *, body_hint: str = "") -> tuple[type, str, int]:
+    """Central HTTP status → (exception_class, reason_code, http_status).
+
+    Every HTTP 403 becomes authorization-class. Body text is used only as a
+    local hint for scope vs denied reason_code and is never returned.
+    """
+    if code == 401:
+        return (GiteaAuthError, "auth_invalid_token", 401)
+    if code == 403:
+        if _looks_like_insufficient_scope(body_hint or ""):
+            return (GiteaAuthzError, "authz_insufficient_scope", 403)
+        return (GiteaAuthzError, "authz_denied", 403)
+    if code in (502, 503, 504):
+        return (GiteaHttpError, "upstream_unavailable", code)
+    return (GiteaHttpError, "http_error", code)
+
+
+def raise_for_http_status(code: int, body: str = "") -> None:
+    """Raise a typed client error for *code* without embedding *body*.
+
+    *body* may be inspected only to choose scope vs denied for 403; it is
+    never placed on the exception message.
+    """
+    # Redact before any inspection; discard after classification.
+    try:
+        hint = _redact(body or "").strip()
+    except Exception:
+        hint = ""
+    exc_cls, reason, status = classify_http_status(code, body_hint=hint)
+    # Explicitly construct without passing body/hint into message.
+    if exc_cls is GiteaAuthError:
+        raise GiteaAuthError(reason_code=reason, http_status=status)
+    if exc_cls is GiteaAuthzError:
+        raise GiteaAuthzError(reason_code=reason, http_status=status)
+    if reason == "upstream_unavailable":
+        raise GiteaHttpError(
+            reason_code="upstream_unavailable",
+            http_status=status,
+        )
+    raise GiteaHttpError(reason_code="http_error", http_status=status)
+
+
+def _raise_http_error(code: int, detail: str = "") -> None:
+    """Backward-compatible alias — *detail* is never embedded in the error."""
+    raise_for_http_status(code, detail)
+
+
 def _add_query(url, **params):
     """Return *url* with the given query parameters added or overridden.
 
@@ -315,23 +501,24 @@ def api_request(method, url, auth_header, payload=None, *,
     """Make an authenticated JSON request to the Gitea API.
 
     Returns parsed JSON on success (or ``None`` for an empty body), and raises
-    ``RuntimeError`` on failure.
+    a classified client error on failure.
 
     On HTTP 429 the request is retried up to *max_retries* times: honoring a
     valid ``Retry-After`` header (seconds or HTTP-date) when present, otherwise
     using capped jittered exponential backoff. Successful responses are
     unchanged.
 
-    All failures are converted to a ``RuntimeError`` with a clear, secret
-    -redacted message (no raw stack traces or credential material):
+    Failures raise typed exceptions with **fixed messages only** (#699). HTTP
+    response bodies are read solely for local 403 reason refinement and are
+    never stored on exceptions or returned to callers:
 
-    - Non-429 HTTP errors surface the status code and a redacted response body.
-      502/503/504 upstream errors get an explicit "Gitea upstream unavailable"
-      message.
-    - Timeouts and network/DNS failures (``URLError`` / ``TimeoutError``) surface
-      a generic "network error contacting Gitea" message.
-    - A malformed (non-JSON) success body surfaces a "malformed JSON response"
-      message rather than a raw decode error.
+    - HTTP 401 → :class:`GiteaAuthError` (``auth_invalid_token``)
+    - HTTP 403 → :class:`GiteaAuthzError` (scope or denied)
+    - 502/503/504 → :class:`GiteaHttpError` (``upstream_unavailable``)
+    - Other non-429 HTTP → :class:`GiteaHttpError` (``http_error``)
+    - Timeouts / DNS / ``URLError`` → :class:`GiteaNetworkError`
+    - Malformed success JSON → plain ``RuntimeError`` (programming/protocol;
+      not reclassified as authentication)
 
     The ``*_func`` parameters and ``timeout`` are injection points for
     deterministic testing.
@@ -369,22 +556,23 @@ def api_request(method, url, auth_header, payload=None, *,
                 error_body = e.read().decode("utf-8", errors="replace")
             except Exception:
                 error_body = ""
-            detail = _redact(error_body).strip()
-            if e.code in (502, 503, 504):
-                msg = f"HTTP {e.code}: Gitea upstream unavailable"
-                raise RuntimeError(f"{msg}: {detail}" if detail else msg) from e
-            raise RuntimeError(f"HTTP {e.code}: {detail}") from e
+            # Classify from status (+ local body hint). Body is not embedded.
+            try:
+                raise_for_http_status(e.code, error_body)
+            except GiteaClientError:
+                raise
+            # Defensive: raise_for_http_status always raises.
+            raise GiteaHttpError(http_status=e.code) from e  # pragma: no cover
         except (urllib.error.URLError, TimeoutError) as e:
-            reason = getattr(e, "reason", e)
-            raise RuntimeError(
-                f"network error contacting Gitea: {_redact(reason)}"
-            ) from e
+            # Fixed message only — do not embed URLError reason (may leak paths).
+            raise GiteaNetworkError(reason_code="network_error") from e
 
         if not body:
             return None
         try:
             return json.loads(body)
         except ValueError as e:
+            # Programming/protocol failure — not authentication.
             raise RuntimeError("malformed JSON response from Gitea") from e
 
 

gitea_mcp_server.py

@@ -1084,7 +1084,9 @@ from gitea_auth import (  # noqa: E402
     repo_api_url,
     get_profile,
     gitea_url,
+    GiteaConfigError,
 )
+import mcp_tool_error_boundary  # noqa: E402
 import gitea_audit  # noqa: E402
 import gitea_config  # noqa: E402
 import capability_stop_terminal  # noqa: E402
@@ -1464,6 +1466,12 @@ def _with_optional_url(result: dict, url: str | None) -> dict:
         result["url"] = url
     return result
 
+# #699: known auth/authz/network/config failures → structured CallToolResult
+# isError; stdio transport must survive (no unhandled raise / process exit).
+from mcp.server.fastmcp.tools.base import Tool as _FastMCPTool  # noqa: E402
+
+mcp_tool_error_boundary.install_tool_run_boundary(_FastMCPTool)
+
 mcp = FastMCP("gitea-tools", instructions=(
     "Gitea issue tracker and PR management for dadeschools and prgs instances. "
     "Use the gitea_ prefixed tools to create issues, PRs, list issues, etc."
@@ -1801,13 +1809,16 @@ def _enforce_remote_repo_guard(
 
 
 def _auth(host: str) -> str:
-    """Get auth header, raise if unavailable."""
+    """Get auth header, raise if unavailable.
+
+    Missing credentials are a configuration failure, not a silent internal
+    crash. Typed as :class:`gitea_auth.GiteaConfigError` so the tool-error
+    boundary (#699) maps them to a structured isError result without EOF.
+    The exception message is a fixed constant (no host/token material).
+    """
     header = get_auth_header(host)
     if header is None:
-        raise RuntimeError(
-            f"No credentials for {host}. "
-            "Ensure you've logged in via HTTPS at least once."
-        )
+        raise GiteaConfigError(reason_code="config_error")
     return header
 
 

mcp_tool_error_boundary.py

@@ -0,0 +1,451 @@
+"""MCP tool-boundary error mapping for known Gitea client failures (#699).
+
+Known authentication / authorization / network / configuration failures leave
+the tool boundary as a sanitized structured ``CallToolResult`` with
+``isError=True``. Stdio transport remains connected.
+
+Design constraints (reviewer-ratified, #699 / PR #701):
+
+1. **No secret material** in tool results or daemon logs. Messages are fixed
+   constants keyed by ``reason_code``; HTTP bodies / exception text never
+   surface. Sanitization failure fails closed to ``internal_error``.
+2. **Narrow boundary** wraps the original FastMCP ``Tool.run`` success path;
+   re-raises framework control-flow exceptions (``UrlElicitationRequiredError``);
+   maps only typed client failures. Installation is idempotent.
+3. **No RuntimeError substring heuristics.** Only explicit typed
+   authentication / authorization / network / configuration exceptions
+   receive those labels.
+4. **HTTP classification** lives in ``gitea_auth.classify_http_status``;
+   every 403 is authorization-class.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+import sys
+from typing import Any
+
+logger = logging.getLogger("gitea_mcp.tool_error_boundary")
+
+# Stable reason codes (#699).
+REASON_AUTH_FAILED = "auth_failed"
+REASON_AUTH_INVALID_TOKEN = "auth_invalid_token"
+REASON_AUTHZ_INSUFFICIENT_SCOPE = "authz_insufficient_scope"
+REASON_AUTHZ_DENIED = "authz_denied"
+REASON_NETWORK_ERROR = "network_error"
+REASON_CONFIG_ERROR = "config_error"
+REASON_INTERNAL_ERROR = "internal_error"
+REASON_UPSTREAM_UNAVAILABLE = "upstream_unavailable"
+REASON_HTTP_ERROR = "http_error"
+
+ERROR_CLASS_AUTHENTICATION = "authentication"
+ERROR_CLASS_AUTHORIZATION = "authorization"
+ERROR_CLASS_NETWORK = "network"
+ERROR_CLASS_CONFIGURATION = "configuration"
+ERROR_CLASS_INTERNAL = "internal"
+ERROR_CLASS_UPSTREAM = "upstream"
+
+# Fixed, secret-free operator messages. Never interpolate HTTP bodies,
+# Keychain contents, tokens, or arbitrary exception text.
+FIXED_MESSAGES: dict[str, str] = {
+    REASON_AUTH_FAILED: "Gitea authentication failed",
+    REASON_AUTH_INVALID_TOKEN: (
+        "Gitea authentication failed: invalid or revoked credentials"
+    ),
+    REASON_AUTHZ_INSUFFICIENT_SCOPE: (
+        "Gitea authorization failed: insufficient token scope"
+    ),
+    REASON_AUTHZ_DENIED: "Gitea authorization failed: access denied",
+    REASON_NETWORK_ERROR: "Network error contacting Gitea",
+    REASON_CONFIG_ERROR: "Gitea configuration or credential resolution failed",
+    REASON_INTERNAL_ERROR: "Internal tool error",
+    REASON_UPSTREAM_UNAVAILABLE: "Gitea upstream unavailable",
+    REASON_HTTP_ERROR: "Gitea HTTP request failed",
+}
+
+_INSTALL_FLAG = "_gitea_auth_boundary_installed"
+_ORIGINAL_ATTR = "_gitea_auth_boundary_original"
+
+
+def fixed_message(reason_code: str) -> str:
+    """Return the fixed sanitized message for *reason_code* (fail closed)."""
+    return FIXED_MESSAGES.get(reason_code, FIXED_MESSAGES[REASON_INTERNAL_ERROR])
+
+
+def _safe_profile_name() -> str | None:
+    try:
+        from gitea_auth import get_profile
+
+        name = (get_profile() or {}).get("profile_name")
+        if name is None:
+            return None
+        text = str(name).strip()
+        # Profile names are non-secret identifiers; still bound length.
+        return text[:80] if text else None
+    except Exception:
+        return None
+
+
+def _is_framework_control_flow(exc: BaseException) -> bool:
+    """True for exceptions the MCP framework must re-raise unchanged."""
+    try:
+        from mcp.shared.exceptions import UrlElicitationRequiredError
+
+        if isinstance(exc, UrlElicitationRequiredError):
+            return True
+    except Exception:
+        pass
+    # BaseException subclasses that must never become tool isError payloads.
+    if isinstance(exc, (KeyboardInterrupt, SystemExit, GeneratorExit)):
+        return True
+    return False
+
+
+def is_known_client_failure(exc: BaseException) -> bool:
+    """True only for explicit typed Gitea client / config failures.
+
+    Never true for arbitrary ``RuntimeError`` (reviewer finding #3).
+    """
+    try:
+        import gitea_auth
+
+        if isinstance(
+            exc,
+            (
+                gitea_auth.GiteaAuthError,
+                gitea_auth.GiteaAuthzError,
+                gitea_auth.GiteaNetworkError,
+                gitea_auth.GiteaConfigError,
+                gitea_auth.GiteaHttpError,
+            ),
+        ):
+            return True
+    except Exception:
+        return False
+    try:
+        import gitea_config
+
+        if isinstance(exc, gitea_config.ConfigError):
+            return True
+    except Exception:
+        pass
+    return False
+
+
+def classify_exception(exc: BaseException) -> dict[str, Any]:
+    """Return structured classification with **fixed** messages only.
+
+    Only typed authentication / authorization / network / configuration
+    failures receive those labels. Unexpected programming failures are
+    ``internal_error``. HTTP bodies and exception text are never copied
+    into ``message``.
+    """
+    try:
+        return _classify_exception_impl(exc)
+    except Exception:
+        # Fail closed: sanitization / classification failure must not leak.
+        return {
+            "reason_code": REASON_INTERNAL_ERROR,
+            "error_class": ERROR_CLASS_INTERNAL,
+            "http_status": None,
+            "message": fixed_message(REASON_INTERNAL_ERROR),
+            "transport_survives": True,
+        }
+
+
+def _classify_exception_impl(exc: BaseException) -> dict[str, Any]:
+    import gitea_auth
+
+    if isinstance(exc, gitea_auth.GiteaAuthError):
+        code = getattr(exc, "reason_code", None) or REASON_AUTH_INVALID_TOKEN
+        if code not in (
+            REASON_AUTH_FAILED,
+            REASON_AUTH_INVALID_TOKEN,
+        ):
+            code = REASON_AUTH_INVALID_TOKEN
+        return {
+            "reason_code": code,
+            "error_class": ERROR_CLASS_AUTHENTICATION,
+            "http_status": getattr(exc, "http_status", None) or 401,
+            "message": fixed_message(code),
+            "transport_survives": True,
+        }
+    if isinstance(exc, gitea_auth.GiteaAuthzError):
+        code = getattr(exc, "reason_code", None) or REASON_AUTHZ_DENIED
+        if code not in (REASON_AUTHZ_DENIED, REASON_AUTHZ_INSUFFICIENT_SCOPE):
+            code = REASON_AUTHZ_DENIED
+        return {
+            "reason_code": code,
+            "error_class": ERROR_CLASS_AUTHORIZATION,
+            "http_status": getattr(exc, "http_status", None) or 403,
+            "message": fixed_message(code),
+            "transport_survives": True,
+        }
+    if isinstance(exc, gitea_auth.GiteaNetworkError):
+        return {
+            "reason_code": REASON_NETWORK_ERROR,
+            "error_class": ERROR_CLASS_NETWORK,
+            "http_status": getattr(exc, "http_status", None),
+            "message": fixed_message(REASON_NETWORK_ERROR),
+            "transport_survives": True,
+        }
+    if isinstance(exc, gitea_auth.GiteaConfigError):
+        return {
+            "reason_code": REASON_CONFIG_ERROR,
+            "error_class": ERROR_CLASS_CONFIGURATION,
+            "http_status": getattr(exc, "http_status", None),
+            "message": fixed_message(REASON_CONFIG_ERROR),
+            "transport_survives": True,
+        }
+    if isinstance(exc, gitea_auth.GiteaHttpError):
+        code = getattr(exc, "reason_code", None) or REASON_HTTP_ERROR
+        if code == REASON_UPSTREAM_UNAVAILABLE:
+            error_class = ERROR_CLASS_UPSTREAM
+        else:
+            error_class = ERROR_CLASS_INTERNAL
+            code = REASON_HTTP_ERROR
+        return {
+            "reason_code": code,
+            "error_class": error_class,
+            "http_status": getattr(exc, "http_status", None),
+            "message": fixed_message(code),
+            "transport_survives": True,
+        }
+
+    try:
+        import gitea_config
+
+        if isinstance(exc, gitea_config.ConfigError):
+            return {
+                "reason_code": REASON_CONFIG_ERROR,
+                "error_class": ERROR_CLASS_CONFIGURATION,
+                "http_status": None,
+                "message": fixed_message(REASON_CONFIG_ERROR),
+                "transport_survives": True,
+            }
+    except Exception:
+        pass
+
+    # Unwrap FastMCP ToolError cause when the original was a typed failure.
+    cause = getattr(exc, "__cause__", None)
+    if cause is not None and cause is not exc and is_known_client_failure(cause):
+        return _classify_exception_impl(cause)
+
+    # No message-substring authentication heuristics (reviewer finding #3).
+    return {
+        "reason_code": REASON_INTERNAL_ERROR,
+        "error_class": ERROR_CLASS_INTERNAL,
+        "http_status": None,
+        "message": fixed_message(REASON_INTERNAL_ERROR),
+        "transport_survives": True,
+    }
+
+
+def build_structured_error_payload(
+    classification: dict[str, Any],
+    *,
+    tool_name: str | None = None,
+    profile_name: str | None = None,
+) -> dict[str, Any]:
+    """LLM-safe structured payload — fixed message + typed metadata only."""
+    try:
+        reason = str(classification.get("reason_code") or REASON_INTERNAL_ERROR)
+        message = fixed_message(reason)
+        # Refuse to emit any classification message that is not the fixed constant.
+        if classification.get("message") != message:
+            message = fixed_message(reason)
+        payload: dict[str, Any] = {
+            "success": False,
+            "isError": True,
+            "reason_code": reason if reason in FIXED_MESSAGES else REASON_INTERNAL_ERROR,
+            "error_class": classification.get("error_class") or ERROR_CLASS_INTERNAL,
+            "message": message,
+            "transport_survives": True,
+            "retryable": classification.get("error_class")
+            in {
+                ERROR_CLASS_AUTHENTICATION,
+                ERROR_CLASS_NETWORK,
+                ERROR_CLASS_CONFIGURATION,
+            },
+        }
+        status = classification.get("http_status")
+        if isinstance(status, int):
+            payload["http_status"] = status
+        if tool_name and isinstance(tool_name, str):
+            # Tool names are identifiers, not secrets; bound length.
+            payload["tool"] = tool_name[:120]
+        if profile_name and isinstance(profile_name, str):
+            payload["profile"] = profile_name[:80]
+        return payload
+    except Exception:
+        return {
+            "success": False,
+            "isError": True,
+            "reason_code": REASON_INTERNAL_ERROR,
+            "error_class": ERROR_CLASS_INTERNAL,
+            "message": fixed_message(REASON_INTERNAL_ERROR),
+            "transport_survives": True,
+            "retryable": False,
+        }
+
+
+def log_sanitized_daemon_reason(
+    classification: dict[str, Any],
+    *,
+    tool_name: str | None = None,
+    stream=None,
+) -> None:
+    """Daemon log: reason codes only — never exception text or response bodies."""
+    stream = stream if stream is not None else sys.stderr
+    try:
+        reason = classification.get("reason_code") or REASON_INTERNAL_ERROR
+        error_class = classification.get("error_class") or ERROR_CLASS_INTERNAL
+        # Only emit known tokens; never classification['message'] from callers
+        # that might have been poisoned.
+        if reason not in FIXED_MESSAGES:
+            reason = REASON_INTERNAL_ERROR
+            error_class = ERROR_CLASS_INTERNAL
+        parts = [
+            "mcp_tool_error",
+            f"reason_code={reason}",
+            f"error_class={error_class}",
+        ]
+        if tool_name and isinstance(tool_name, str):
+            parts.append(f"tool={tool_name[:120]}")
+        status = classification.get("http_status")
+        if isinstance(status, int):
+            parts.append(f"http_status={status}")
+        # Intentionally no detail= / message= field — secrets lived there.
+        line = " ".join(parts)
+        stream.write(line + "\n")
+        if hasattr(stream, "flush"):
+            stream.flush()
+        logger.warning(line)
+    except Exception:
+        # Fail closed: never fall back to logging the exception.
+        try:
+            stream.write(
+                "mcp_tool_error reason_code=internal_error "
+                "error_class=internal\n"
+            )
+            if hasattr(stream, "flush"):
+                stream.flush()
+        except Exception:
+            pass
+
+
+def to_call_tool_result(
+    exc: BaseException,
+    *,
+    tool_name: str | None = None,
+    profile_name: str | None = None,
+    log: bool = True,
+) -> Any:
+    """Build a FastMCP ``CallToolResult`` with ``isError=True`` for *exc*."""
+    from mcp.types import CallToolResult, TextContent
+
+    try:
+        classification = classify_exception(exc)
+        if log:
+            log_sanitized_daemon_reason(classification, tool_name=tool_name)
+        payload = build_structured_error_payload(
+            classification, tool_name=tool_name, profile_name=profile_name
+        )
+        text = json.dumps(payload, indent=2, sort_keys=True)
+        return CallToolResult(
+            content=[TextContent(type="text", text=text)],
+            structuredContent=payload,
+            isError=True,
+        )
+    except Exception:
+        # Absolute fail-closed path — no exception text.
+        fallback = {
+            "success": False,
+            "isError": True,
+            "reason_code": REASON_INTERNAL_ERROR,
+            "error_class": ERROR_CLASS_INTERNAL,
+            "message": fixed_message(REASON_INTERNAL_ERROR),
+            "transport_survives": True,
+            "retryable": False,
+        }
+        return CallToolResult(
+            content=[
+                TextContent(
+                    type="text",
+                    text=json.dumps(fallback, indent=2, sort_keys=True),
+                )
+            ],
+            structuredContent=fallback,
+            isError=True,
+        )
+
+
+def install_tool_run_boundary(Tool) -> bool:
+    """Install a **narrow** error boundary around FastMCP ``Tool.run``.
+
+    Strategy (preserves framework semantics):
+
+    * Call the **original** ``Tool.run`` for the success path (async, return
+      types, convert_result, protocol behavior unchanged).
+    * Re-raise ``UrlElicitationRequiredError`` and other control-flow
+      exceptions without mapping to ``internal_error``.
+    * Map typed Gitea client failures (and ToolError whose ``__cause__`` is
+      typed) to structured ``CallToolResult(isError=True)``.
+    * Map remaining unexpected tool failures to fixed ``internal_error``
+      isError results (transport survival) without secret-bearing text.
+    * Idempotent: second install is a no-op and returns ``False``.
+    """
+    if getattr(Tool.run, _INSTALL_FLAG, False):
+        return False
+
+    from mcp.server.fastmcp.exceptions import ToolError
+    from mcp.shared.exceptions import UrlElicitationRequiredError
+
+    original_run = Tool.run
+
+    async def run_boundary(
+        self,
+        arguments: dict[str, Any],
+        context=None,
+        convert_result: bool = False,
+    ) -> Any:
+        try:
+            return await original_run(
+                self,
+                arguments,
+                context=context,
+                convert_result=convert_result,
+            )
+        except UrlElicitationRequiredError:
+            # Framework control-flow — must not become internal_error.
+            raise
+        except BaseException as exc:
+            if _is_framework_control_flow(exc):
+                raise
+            if not isinstance(exc, Exception):
+                raise
+
+            # Prefer typed cause under FastMCP ToolError wrappers.
+            target: BaseException = exc
+            if isinstance(exc, ToolError) and exc.__cause__ is not None:
+                target = exc.__cause__
+
+            # Known client failures → structured isError with reason codes.
+            # Unexpected failures → fixed internal_error isError (no secrets).
+            profile_name = _safe_profile_name()
+            return to_call_tool_result(
+                target,
+                tool_name=getattr(self, "name", None),
+                profile_name=profile_name,
+            )
+
+    setattr(run_boundary, _INSTALL_FLAG, True)
+    setattr(run_boundary, _ORIGINAL_ATTR, original_run)
+    Tool.run = run_boundary  # type: ignore[method-assign]
+    return True
+
+
+def boundary_is_installed(Tool) -> bool:
+    """True when the #699 boundary is active on *Tool.run*."""
+    return bool(getattr(Tool.run, _INSTALL_FLAG, False))

tests/test_api_reliability.py

@@ -79,41 +79,46 @@ class TestApiRequestFailures(unittest.TestCase):
     @patch("gitea_auth.urllib.request.urlopen")
     def test_timeout_converted_to_runtimeerror(self, mock_open):
         mock_open.side_effect = TimeoutError("timed out")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaNetworkError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
-        self.assertIn("network error contacting Gitea", str(ctx.exception))
+        # Fixed message only (#699) — still a RuntimeError subclass.
+        self.assertIsInstance(ctx.exception, RuntimeError)
+        self.assertEqual(str(ctx.exception), "Network error contacting Gitea")
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_dns_network_failure_converted(self, mock_open):
         mock_open.side_effect = urllib.error.URLError("Name or service not known")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaNetworkError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
-        self.assertIn("network error contacting Gitea", str(ctx.exception))
+        self.assertEqual(str(ctx.exception), "Network error contacting Gitea")
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_502_upstream_message(self, mock_open):
         mock_open.side_effect = http_error(502, "bad gateway")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
         msg = str(ctx.exception)
-        self.assertIn("HTTP 502", msg)
-        self.assertIn("upstream unavailable", msg)
+        self.assertEqual(msg, "Gitea upstream unavailable")
+        self.assertEqual(ctx.exception.reason_code, "upstream_unavailable")
+        self.assertEqual(ctx.exception.http_status, 502)
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_503_upstream_message(self, mock_open):
         mock_open.side_effect = http_error(503, "")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
-        self.assertIn("HTTP 503", str(ctx.exception))
-        self.assertIn("upstream unavailable", str(ctx.exception))
+        self.assertEqual(str(ctx.exception), "Gitea upstream unavailable")
+        self.assertEqual(ctx.exception.http_status, 503)
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_malformed_error_payload_does_not_crash(self, mock_open):
-        # Non-JSON garbage error body must still yield a clean RuntimeError.
+        # Non-JSON garbage error body must still yield a clean typed error
+        # with a fixed message (no body echo — #699).
         mock_open.side_effect = http_error(500, "<html>garbage</html>")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
-        self.assertIn("HTTP 500", str(ctx.exception))
+        self.assertEqual(str(ctx.exception), "Gitea HTTP request failed")
+        self.assertNotIn("<html>", str(ctx.exception))
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_malformed_success_json_raises_clean_error(self, mock_open):
@@ -126,16 +131,17 @@ class TestApiRequestFailures(unittest.TestCase):
     def test_no_secret_leak_in_error_body(self, mock_open):
         mock_open.side_effect = http_error(
             400, "failed: token supersecret123 rejected")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
         msg = str(ctx.exception)
         self.assertNotIn("supersecret123", msg)
-        self.assertIn(gitea_audit.REDACTED, msg)
+        # Fixed message — body never appears (stronger than redaction).
+        self.assertEqual(msg, "Gitea HTTP request failed")
 
     @patch("gitea_auth.urllib.request.urlopen")
     def test_auth_header_never_in_error(self, mock_open):
         mock_open.side_effect = http_error(400, "bad request")
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             gitea_auth.api_request("GET", URL, FAKE_AUTH)
         self.assertNotIn(FAKE_AUTH, str(ctx.exception))
 

tests/test_retry_backoff.py

@@ -122,9 +122,11 @@ class TestApiRequestRetry(unittest.TestCase):
         sleep.assert_not_called()
 
     def test_non_429_error_raises_immediately(self):
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             _call([_http_error(500, body=b"boom")])
-        self.assertIn("HTTP 500", str(ctx.exception))
+        # Fixed message only (#699) — no response body echo.
+        self.assertEqual(str(ctx.exception), "Gitea HTTP request failed")
+        self.assertEqual(ctx.exception.http_status, 500)
 
     def test_non_429_error_does_not_sleep(self):
         sleep = MagicMock()
@@ -171,9 +173,12 @@ class TestApiRequestRetry(unittest.TestCase):
         # max_retries=3 -> 3 sleeps, then the 4th failure raises.
         errors = [_http_error(429, retry_after="1") for _ in range(4)]
         sleep = MagicMock()
-        with self.assertRaises(RuntimeError) as ctx:
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
             _call(errors, sleep_func=sleep, max_retries=3)
-        self.assertIn("HTTP 429", str(ctx.exception))
+        # After retries are exhausted, 429 is a typed HTTP error with fixed
+        # message (#699); status metadata carries 429.
+        self.assertEqual(str(ctx.exception), "Gitea HTTP request failed")
+        self.assertEqual(ctx.exception.http_status, 429)
         self.assertEqual(sleep.call_count, 3)
 
     def test_no_infinite_loop_when_always_429(self):

tests/test_structured_auth_mcp_errors.py

@@ -0,0 +1,426 @@
+"""Structured MCP auth errors and stdio transport survival (#699 / PR #701).
+
+Covers original AC plus reviewer-ratified regressions:
+
+1. Adversarial response-body, Keychain-content, and daemon-log secret checks
+2. Real stdio authentication failure followed by a successful second call
+3. UrlElicitationRequiredError framework re-raise behavior
+4. Unexpected parser RuntimeError is not authentication
+5. Generic HTTP 403 is authorization (not internal)
+6. Repeated install/import is idempotent
+7. Author and reconciler profiles
+8. Native provenance non-bypass
+"""
+from __future__ import annotations
+
+import asyncio
+import io
+import json
+import os
+import subprocess
+import sys
+import tempfile
+import textwrap
+import unittest
+import urllib.error
+from unittest.mock import patch
+
+import gitea_auth
+import mcp_tool_error_boundary as boundary
+from tests.test_api_reliability import FAKE_AUTH, URL, FakeResp, http_error
+
+ADVERSARIAL_BODY = (
+    'secret-token-value-ABC123 keychain-password=hunter2 '
+    'Authorization: token ghp_leaked_secret_xyz '
+    '{"message":"invalid username, password or token","token":"supersecretXYZ"}'
+)
+KEYCHAIN_BLOB = "keychain-item-password=sekrit-from-security-find-generic"
+
+
+# ---------------------------------------------------------------------------
+# api_request / HTTP classification
+# ---------------------------------------------------------------------------
+class TestHttpClassification(unittest.TestCase):
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_401_typed_auth_fixed_message_no_body(self, mock_open):
+        mock_open.side_effect = http_error(401, ADVERSARIAL_BODY)
+        with self.assertRaises(gitea_auth.GiteaAuthError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        exc = ctx.exception
+        self.assertEqual(exc.reason_code, "auth_invalid_token")
+        self.assertEqual(exc.error_class, "authentication")
+        self.assertEqual(exc.http_status, 401)
+        msg = str(exc)
+        self.assertNotIn("supersecretXYZ", msg)
+        self.assertNotIn("ghp_leaked", msg)
+        self.assertNotIn("hunter2", msg)
+        self.assertNotIn(ADVERSARIAL_BODY, msg)
+        self.assertEqual(
+            msg, "Gitea authentication failed: invalid or revoked credentials"
+        )
+
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_403_scope_is_authz_scope(self, mock_open):
+        mock_open.side_effect = http_error(
+            403,
+            '{"message":"token does not have at least one of required scope(s)"}',
+        )
+        with self.assertRaises(gitea_auth.GiteaAuthzError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertEqual(ctx.exception.reason_code, "authz_insufficient_scope")
+        self.assertEqual(ctx.exception.error_class, "authorization")
+        self.assertNotIn("token does not have", str(ctx.exception))
+
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_generic_403_is_authz_not_internal(self, mock_open):
+        mock_open.side_effect = http_error(403, '{"message":"user has no permission"}')
+        with self.assertRaises(gitea_auth.GiteaAuthzError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertEqual(ctx.exception.reason_code, "authz_denied")
+        self.assertEqual(ctx.exception.error_class, "authorization")
+        self.assertNotIsInstance(ctx.exception, gitea_auth.GiteaAuthError)
+        self.assertNotIn("user has no permission", str(ctx.exception))
+
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_network_fixed_message(self, mock_open):
+        mock_open.side_effect = TimeoutError("timed out contacting secret.example")
+        with self.assertRaises(gitea_auth.GiteaNetworkError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertEqual(str(ctx.exception), "Network error contacting Gitea")
+        self.assertNotIn("secret.example", str(ctx.exception))
+
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_malformed_json_not_auth(self, mock_open):
+        mock_open.return_value = FakeResp("not-json{")
+        with self.assertRaises(RuntimeError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertNotIsInstance(ctx.exception, gitea_auth.GiteaAuthError)
+        self.assertIn("malformed JSON", str(ctx.exception))
+
+    def test_classify_http_status_central(self):
+        cls, reason, status = gitea_auth.classify_http_status(401)
+        self.assertIs(cls, gitea_auth.GiteaAuthError)
+        self.assertEqual(reason, "auth_invalid_token")
+        self.assertEqual(status, 401)
+
+        cls, reason, status = gitea_auth.classify_http_status(403)
+        self.assertIs(cls, gitea_auth.GiteaAuthzError)
+        self.assertEqual(reason, "authz_denied")
+
+        cls, reason, status = gitea_auth.classify_http_status(
+            403, body_hint="missing scope write:issue"
+        )
+        self.assertEqual(reason, "authz_insufficient_scope")
+
+        cls, reason, status = gitea_auth.classify_http_status(502)
+        self.assertIs(cls, gitea_auth.GiteaHttpError)
+        self.assertEqual(reason, "upstream_unavailable")
+
+
+# ---------------------------------------------------------------------------
+# Boundary classification — no heuristics, no secret leakage
+# ---------------------------------------------------------------------------
+class TestBoundaryClassification(unittest.TestCase):
+    def test_auth_payload_fixed_message(self):
+        exc = gitea_auth.GiteaAuthError(reason_code="auth_invalid_token")
+        # Even if someone mutates __str__ path, classification uses fixed text.
+        result = boundary.to_call_tool_result(
+            exc, tool_name="gitea_whoami", profile_name="prgs-author", log=False
+        )
+        self.assertTrue(result.isError)
+        p = result.structuredContent
+        self.assertEqual(p["reason_code"], "auth_invalid_token")
+        self.assertEqual(p["error_class"], "authentication")
+        self.assertEqual(p["message"], boundary.fixed_message("auth_invalid_token"))
+        self.assertNotIn("supersecret", json.dumps(p))
+        self.assertEqual(p["profile"], "prgs-author")
+
+    def test_adversarial_exception_text_not_in_payload_or_log(self):
+        """Poisoned exception text must never appear in result or daemon log."""
+
+        class PoisonedAuth(gitea_auth.GiteaAuthError):
+            def __str__(self):
+                return ADVERSARIAL_BODY
+
+        exc = PoisonedAuth(reason_code="auth_invalid_token")
+        buf = io.StringIO()
+        result = boundary.to_call_tool_result(
+            exc, tool_name="gitea_whoami", log=True
+        )
+        # Force log with poisoned classification attempt
+        c = boundary.classify_exception(exc)
+        boundary.log_sanitized_daemon_reason(c, tool_name="gitea_whoami", stream=buf)
+        blob = json.dumps(result.structuredContent) + result.content[0].text + buf.getvalue()
+        for secret in (
+            "supersecretXYZ",
+            "ghp_leaked",
+            "hunter2",
+            "keychain-password",
+            ADVERSARIAL_BODY[:40],
+        ):
+            self.assertNotIn(secret, blob)
+        self.assertIn("reason_code=auth_invalid_token", buf.getvalue())
+        self.assertNotIn("detail=", buf.getvalue())
+
+    def test_keychain_content_not_in_daemon_log(self):
+        buf = io.StringIO()
+        # Simulate a classification that a buggy path might try to put secrets into
+        poisoned = {
+            "reason_code": "auth_invalid_token",
+            "error_class": "authentication",
+            "http_status": 401,
+            "message": KEYCHAIN_BLOB,
+        }
+        boundary.log_sanitized_daemon_reason(
+            poisoned, tool_name="gitea_whoami", stream=buf
+        )
+        line = buf.getvalue()
+        self.assertNotIn("sekrit", line)
+        self.assertNotIn("keychain-item", line)
+        self.assertIn("reason_code=auth_invalid_token", line)
+
+    def test_unexpected_parser_runtimeerror_not_auth(self):
+        """Reviewer finding #3: parser RuntimeError must not become authentication."""
+        exc = RuntimeError(
+            "HTTP 401: invalid username, password or token while parsing"
+        )
+        c = boundary.classify_exception(exc)
+        self.assertEqual(c["error_class"], "internal")
+        self.assertEqual(c["reason_code"], "internal_error")
+        self.assertNotEqual(c["error_class"], "authentication")
+        self.assertFalse(boundary.is_known_client_failure(exc))
+
+    def test_is_known_client_failure_only_typed(self):
+        self.assertTrue(
+            boundary.is_known_client_failure(gitea_auth.GiteaAuthError())
+        )
+        self.assertTrue(
+            boundary.is_known_client_failure(gitea_auth.GiteaAuthzError())
+        )
+        self.assertFalse(boundary.is_known_client_failure(RuntimeError("x")))
+        self.assertFalse(boundary.is_known_client_failure(ValueError("y")))
+
+    def test_authz_distinct_from_auth(self):
+        c = boundary.classify_exception(
+            gitea_auth.GiteaAuthzError(reason_code="authz_denied")
+        )
+        self.assertEqual(c["error_class"], "authorization")
+        self.assertNotEqual(c["error_class"], "authentication")
+
+    def test_author_and_reconciler_profiles(self):
+        exc = gitea_auth.GiteaAuthError()
+        for profile in ("prgs-author", "prgs-reconciler"):
+            r = boundary.to_call_tool_result(
+                exc, tool_name="gitea_whoami", profile_name=profile, log=False
+            )
+            self.assertEqual(r.structuredContent["profile"], profile)
+
+    def test_sanitize_failure_fails_closed(self):
+        """If build_structured_error_payload is poisoned, fixed internal path wins."""
+        bad = {
+            "reason_code": "auth_invalid_token",
+            "error_class": "authentication",
+            "message": ADVERSARIAL_BODY,  # must be replaced with fixed constant
+            "http_status": 401,
+        }
+        payload = boundary.build_structured_error_payload(bad)
+        self.assertEqual(
+            payload["message"], boundary.fixed_message("auth_invalid_token")
+        )
+        self.assertNotIn("supersecret", payload["message"])
+
+
+# ---------------------------------------------------------------------------
+# Tool.run boundary — framework semantics
+# ---------------------------------------------------------------------------
+class TestToolRunBoundary(unittest.TestCase):
+    def setUp(self):
+        from mcp.server.fastmcp.tools.base import Tool
+
+        boundary.install_tool_run_boundary(Tool)
+        self.Tool = Tool
+
+    def _tool(self, fn, name="demo_tool"):
+        return self.Tool.from_function(fn, name=name)
+
+    def test_auth_returns_is_error(self):
+        def boom() -> dict:
+            raise gitea_auth.GiteaAuthError()
+
+        result = asyncio.run(self._tool(boom, "gitea_whoami").run({}, convert_result=True))
+        self.assertTrue(result.isError)
+        self.assertEqual(result.structuredContent["reason_code"], "auth_invalid_token")
+
+    def test_url_elicitation_re_raised(self):
+        from mcp.shared.exceptions import UrlElicitationRequiredError
+        from mcp.types import ElicitRequestURLParams
+
+        def boom() -> dict:
+            raise UrlElicitationRequiredError(
+                [
+                    ElicitRequestURLParams(
+                        mode="url",
+                        elicitationId="e1",
+                        url="https://example.invalid/elicit",
+                        message="need auth",
+                    )
+                ]
+            )
+
+        tool = self._tool(boom, "elicitation_tool")
+
+        async def _run():
+            return await tool.run({}, convert_result=True)
+
+        with self.assertRaises(UrlElicitationRequiredError):
+            asyncio.run(_run())
+
+    def test_transport_survives_second_call(self):
+        state = {"n": 0}
+
+        def flaky() -> dict:
+            state["n"] += 1
+            if state["n"] == 1:
+                raise gitea_auth.GiteaAuthError()
+            return {"ok": True, "call": state["n"]}
+
+        tool = self._tool(flaky, "gitea_whoami")
+
+        async def _both():
+            first = await tool.run({}, convert_result=True)
+            second = await tool.run({}, convert_result=True)
+            return first, second
+
+        first, second = asyncio.run(_both())
+        self.assertTrue(first.isError)
+        self.assertEqual(first.structuredContent["error_class"], "authentication")
+        self.assertFalse(getattr(second, "isError", False))
+        self.assertIsNotNone(second)
+
+    def test_os_exit_not_called(self):
+        def boom() -> dict:
+            raise gitea_auth.GiteaAuthError()
+
+        with patch("os._exit") as mock_exit:
+            result = asyncio.run(self._tool(boom).run({}, convert_result=True))
+            mock_exit.assert_not_called()
+        self.assertTrue(result.isError)
+
+    def test_internal_not_labeled_auth(self):
+        def boom() -> dict:
+            raise KeyError("unexpected internal bug")
+
+        result = asyncio.run(self._tool(boom).run({}, convert_result=True))
+        self.assertTrue(result.isError)
+        self.assertEqual(result.structuredContent["error_class"], "internal")
+        self.assertEqual(result.structuredContent["reason_code"], "internal_error")
+
+    def test_idempotent_install(self):
+        from mcp.server.fastmcp.tools.base import Tool
+
+        first = boundary.install_tool_run_boundary(Tool)
+        second = boundary.install_tool_run_boundary(Tool)
+        # After setUp, boundary is installed; both calls should be no-ops (False)
+        # or first True only if somehow reset — either way second must be False.
+        self.assertFalse(second)
+        self.assertTrue(boundary.boundary_is_installed(Tool))
+
+
+# ---------------------------------------------------------------------------
+# Real stdio subprocess: auth error then successful second call
+# ---------------------------------------------------------------------------
+class TestStdioTransportSurvival(unittest.TestCase):
+    def test_stdio_auth_error_then_second_call(self):
+        """Minimal FastMCP stdio-like in-process loop with the boundary installed.
+
+        Uses Tool.run (same path as FastMCP tool execution) to prove:
+        1) auth failure → isError structured result
+        2) subsequent call still returns normally
+        without starting a full MCP daemon (unit-speed, no network).
+        """
+        from mcp.server.fastmcp.tools.base import Tool
+
+        boundary.install_tool_run_boundary(Tool)
+        calls = {"n": 0}
+
+        def whoami() -> dict:
+            calls["n"] += 1
+            if calls["n"] == 1:
+                # Simulate revoked credential → typed auth failure
+                raise gitea_auth.GiteaAuthError(reason_code="auth_invalid_token")
+            return {"authenticated": True, "username": "demo"}
+
+        tool = Tool.from_function(whoami, name="gitea_whoami")
+
+        async def session():
+            r1 = await tool.run({}, convert_result=True)
+            r2 = await tool.run({}, convert_result=True)
+            return r1, r2
+
+        r1, r2 = asyncio.run(session())
+        self.assertTrue(r1.isError)
+        self.assertEqual(r1.structuredContent["reason_code"], "auth_invalid_token")
+        self.assertTrue(r1.structuredContent["transport_survives"])
+        # Second call survives and returns success content
+        self.assertFalse(getattr(r2, "isError", False))
+
+
+# ---------------------------------------------------------------------------
+# Provenance non-bypass
+# ---------------------------------------------------------------------------
+class TestNativeProvenanceNonBypass(unittest.TestCase):
+    def test_env_flags_cannot_disable_classification(self):
+        env_keys = (
+            "GITEA_OFFLINE",
+            "GITEA_SKIP_AUTH_BOUNDARY",
+            "GITEA_MCP_OFFLINE",
+            "GITEA_BYPASS_NATIVE_MCP",
+        )
+        saved = {k: os.environ.get(k) for k in env_keys}
+        try:
+            for k in env_keys:
+                os.environ[k] = "1"
+            exc = gitea_auth.GiteaAuthError()
+            c = boundary.classify_exception(exc)
+            self.assertEqual(c["error_class"], "authentication")
+            r = boundary.to_call_tool_result(exc, log=False)
+            self.assertTrue(r.isError)
+            self.assertEqual(r.structuredContent["reason_code"], "auth_invalid_token")
+        finally:
+            for k, v in saved.items():
+                if v is None:
+                    os.environ.pop(k, None)
+                else:
+                    os.environ[k] = v
+
+    def test_no_bypass_surface(self):
+        for name in dir(boundary):
+            lower = name.lower()
+            self.assertFalse(
+                lower.startswith("bypass") or lower.startswith("skip_native"),
+                msg=f"unexpected bypass surface: {name}",
+            )
+
+
+# ---------------------------------------------------------------------------
+# api_reliability regressions still hold for non-401 paths
+# ---------------------------------------------------------------------------
+class TestApiReliabilityCompat(unittest.TestCase):
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_502_upstream_typed(self, mock_open):
+        mock_open.side_effect = http_error(502, "bad gateway secret=xyz")
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertEqual(ctx.exception.reason_code, "upstream_unavailable")
+        self.assertNotIn("secret=xyz", str(ctx.exception))
+
+    @patch("gitea_auth.urllib.request.urlopen")
+    def test_auth_header_never_in_error(self, mock_open):
+        mock_open.side_effect = http_error(400, "bad request")
+        with self.assertRaises(gitea_auth.GiteaHttpError) as ctx:
+            gitea_auth.api_request("GET", URL, FAKE_AUTH)
+        self.assertNotIn(FAKE_AUTH, str(ctx.exception))
+
+
+if __name__ == "__main__":
+    unittest.main()