diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9de5a282..cfe56f74 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ the frozen-backend fallback mirror it for their toolchains.
 ## [Unreleased]
 
 **Highlights**
+- A failure with no stage attached no longer borrows another stage's advice, so a text-to-speech error stops telling you the video server dropped the download (#1943)
+- A generation failure that the app cannot classify now names the backend error class, so two unrelated faults stop arriving as the same untriageable report (#1800)
 
 - Transcriptions dictation wakes the desktop recorder, presents one contextual start action, and centers its microphone icon with the label (#1902)
 - Apple Silicon now shows one canonical OmniVoice choice in the engine picker while retaining its automatic crash-isolated sidecar runtime (#1913)
@@ -58,6 +60,7 @@ the frozen-backend fallback mirror it for their toolchains.
 
 ### Fixed
 
+- Windows desktop launches no longer freeze at "Loading ML runtime (PyTorch)": the parent-liveness watchdog polls the stdin pipe instead of leaving a read pending, which deadlocked numpy's OpenBLAS initializer (#1955)
 - Voice synthesis progress no longer races to a fabricated 95%; it stays indeterminate until the active generation path reports real progress (#1907) — thanks @psiberfunk!
 - Long audiobook chapters now use the same device- and text-length-aware synthesis timeout as other TTS routes (#1910) — thanks @psiberfunk!
 
diff --git a/backend/core/failure.py b/backend/core/failure.py
index 2930ad20..21fd815f 100644
--- a/backend/core/failure.py
+++ b/backend/core/failure.py
@@ -308,6 +308,13 @@ _CONTEXT_FREE_HINT_CLASSES = frozenset({
     # a Windows virtual-memory setting rather than a connectivity problem, and
     # the detailed hint we already had for it never reached them.
     "WINDOWS_PAGING_FILE_TOO_SMALL",
+    # Its trigger is a VoiceStudio-authored sentence — "the TTS model cache
+    # for … is incomplete" plus "could not be auto-repaired" / "weights
+    # missing" — so it cannot be produced by an unrelated library. The 500
+    # handler is the surface a corrupt cache actually reaches, and dropping
+    # its hint there would leave the user with no way to know a redownload
+    # is the fix.
+    "MODEL_CACHE_CORRUPT",
 })
 
 
diff --git a/backend/core/parent_liveness.py b/backend/core/parent_liveness.py
index e6707752..523e894a 100644
--- a/backend/core/parent_liveness.py
+++ b/backend/core/parent_liveness.py
@@ -4,7 +4,14 @@ from __future__ import annotations
 import os
 import sys
 import threading
-from typing import BinaryIO, Callable
+import time
+from typing import Any, BinaryIO, Callable, Optional
+
+# Poll cadence for the Windows pipe watcher. Exit latency after the desktop
+# closes its end is bounded by this; the desktop's own kill-on-close Job is the
+# hard backstop, so a quarter second is plenty and costs nothing measurable.
+WINDOWS_PIPE_POLL_INTERVAL_S = 0.25
+_FILE_TYPE_PIPE = 3  # winbase.h FILE_TYPE_PIPE
 
 
 def _watch_parent_pipe(reader: BinaryIO, exit_process: Callable[[int], None]) -> None:
@@ -18,6 +25,64 @@ def _watch_parent_pipe(reader: BinaryIO, exit_process: Callable[[int], None]) ->
     exit_process(0)
 
 
+def _watch_parent_pipe_handle(
+    handle: int,
+    exit_process: Callable[[int], None],
+    *,
+    peek: Optional[Callable[[int], Any]] = None,
+    read_file: Optional[Callable[[int, int], Any]] = None,
+    sleep: Callable[[float], None] = time.sleep,
+    interval: float = WINDOWS_PIPE_POLL_INTERVAL_S,
+) -> None:
+    """Windows twin of :func:`_watch_parent_pipe` that never leaves a read
+    pending on the pipe.
+
+    A synchronous ``ReadFile`` parked on the stdin pipe — whether issued through
+    the C runtime's ``read()`` or straight to the kernel — deadlocks the
+    OpenBLAS DLL initializer that ``import torch`` reaches (numpy's
+    ``_multiarray_umath``) in the startup worker: every desktop-spawned backend
+    on Windows froze at "Loading ML runtime (PyTorch)" while the identical
+    command from a terminal, with no stdin pipe and no watchdog, started in
+    seconds. A thread that merely sleeps does not trigger it; only the pending
+    read on that pipe does. So instead of blocking in a read, poll with
+    ``PeekNamedPipe``: it returns immediately, holds no I/O on the file object,
+    drains any keepalive bytes the desktop might write, and fails with
+    ``ERROR_BROKEN_PIPE`` the moment the desktop closes its end — which is the
+    same EOF signal the POSIX reader gets.
+    """
+    if peek is None or read_file is None:
+        import _winapi  # Windows-only stdlib module; the caller gates on the platform
+
+        peek = peek or _winapi.PeekNamedPipe
+        read_file = read_file or _winapi.ReadFile
+    try:
+        while True:
+            available, _ = peek(handle)
+            if available:
+                # Bytes are already buffered, so this read cannot block.
+                read_file(handle, available)
+            else:
+                sleep(interval)
+    except OSError:
+        # ERROR_BROKEN_PIPE (109) is how the closed parent end surfaces here.
+        pass
+    exit_process(0)
+
+
+def _windows_pipe_handle(reader: Any) -> Optional[int]:
+    """The OS handle behind ``reader`` when it is a pipe, else None."""
+    try:
+        import msvcrt
+        import _winapi
+
+        handle = msvcrt.get_osfhandle(reader.fileno())
+        if _winapi.GetFileType(handle) != _FILE_TYPE_PIPE:
+            return None
+        return handle
+    except (OSError, ValueError, AttributeError, ImportError):
+        return None
+
+
 def arm_desktop_parent_watchdog() -> bool:
     """Use stdin EOF as an unforgeable parent-liveness signal for desktop runs."""
     if os.environ.get("OMNIVOICE_DESKTOP_CONTAINED") != "1":
@@ -25,9 +90,18 @@ def arm_desktop_parent_watchdog() -> bool:
     reader = getattr(sys.stdin, "buffer", None)
     if reader is None:
         return False
+    target: Callable[..., None] = _watch_parent_pipe
+    args: tuple = (reader, os._exit)
+    if os.name == "nt":
+        handle = _windows_pipe_handle(reader)
+        if handle is not None:
+            target = _watch_parent_pipe_handle
+            args = (handle, os._exit)
+        # A non-pipe stdin (file, NUL) cannot have a read pending against a
+        # pipe file object, so the blocking reader stays correct there.
     threading.Thread(
-        target=_watch_parent_pipe,
-        args=(reader, os._exit),
+        target=target,
+        args=args,
         name="desktop-parent-watchdog",
         daemon=True,
     ).start()
diff --git a/backend/core/public_errors.py b/backend/core/public_errors.py
index e5ad1499..91501c08 100644
--- a/backend/core/public_errors.py
+++ b/backend/core/public_errors.py
@@ -94,6 +94,16 @@ def stream_generation_failure(error: BaseException | object) -> dict[str, object
     replace the failure being diagnosed.
     """
     payload = stream_failure("generation_failed")
+    if isinstance(error, BaseException):
+        # The exception's TYPE NAME, never its message. Two failures that both
+        # render the floor message "Generation failed. Check the selected
+        # engine and try again." are indistinguishable in an auto-filed report,
+        # so every unclassified streaming failure arrives as the same issue and
+        # none of them can be triaged (#1800). A class name is VoiceStudio-safe
+        # by the same reasoning that already puts it on the wire as
+        # `error_class` in the dub routes and on the analytics allowlist: it is
+        # a Python type, not user text, and no substring of `error` is copied.
+        payload["error_class"] = type(error).__name__
     try:
         enriched = public_exception_response(error, fallback=str(payload["detail"]))
     except Exception:
@@ -149,12 +159,31 @@ def public_exception_response(error: BaseException, *, fallback: str) -> dict[st
     Classification may inspect the private diagnostic locally, but response
     values come exclusively from VoiceStudio-owned constants. No substring of
     ``error`` is copied into the payload.
+
+    Every caller is a CONTEXT-FREE surface — the global 500 handler, the
+    streaming generate error frame, the dub GPU-OOM 503 — so the topic is
+    filtered through ``failure._CONTEXT_FREE_HINT_CLASSES`` before its hint is
+    attached. Without that filter a topic whose trigger is a generic phrase
+    stamps a confidently wrong remediation on an unrelated failure: #1943 is a
+    macOS mlx-audio TTS 500 that came back advising the user that "the
+    connection to the video server dropped mid-download", because
+    VIDEO_DOWNLOAD_NETWORK triggers on a bare "timed out" / "connection
+    reset". The allowlist already existed and already named that class as the
+    example of what must not appear here; only :func:`failure.append_hint`
+    honoured it, and this helper replaced ``append_hint`` on the 500 path
+    without carrying the rule across.
+
+    HF_MIRROR_UNREACHABLE is allowed alongside it: its hint is dynamic (it
+    names the configured mirror) and its trigger requires that a mirror is
+    configured at all, so it cannot fire on an unrelated failure (#874).
     """
-    from core.failure import classify, public_hint_for_topic
+    from core.failure import _CONTEXT_FREE_HINT_CLASSES, classify, public_hint_for_topic
 
     try:
         topic = classify(str(error))
-        hint = public_hint_for_topic(topic)
+        if topic and topic not in _CONTEXT_FREE_HINT_CLASSES and topic != "HF_MIRROR_UNREACHABLE":
+            topic = ""
+        hint = public_hint_for_topic(topic) if topic else ""
     except Exception:
         topic = ""
         hint = ""
diff --git a/frontend/src/test/streamingTts.test.js b/frontend/src/test/streamingTts.test.js
index e09748b8..6931e73a 100644
--- a/frontend/src/test/streamingTts.test.js
+++ b/frontend/src/test/streamingTts.test.js
@@ -329,6 +329,31 @@ describe('streamGenerateSpeech', () => {
     expect(FakeAudioContext.instances[0].state).toBe('closed');
   });
 
+  it('carries the backend error class from the error frame (#1800)', async () => {
+    // Every unclassified engine failure renders the same floor message, so
+    // the auto-filed reports were byte-identical and none could be triaged.
+    // The class name is the only thing that separates them.
+    apiFetch.mockResolvedValue(
+      ndjsonResponse([
+        startEvent(3),
+        chunkEvent(0),
+        { type: 'error', detail: 'Generation failed.', error_class: 'MemoryError' },
+      ]),
+    );
+    await expect(streamGenerateSpeech(new FormData(), {})).rejects.toMatchObject({
+      errorClass: 'MemoryError',
+    });
+  });
+
+  it('leaves the error class null when the frame omits it', async () => {
+    apiFetch.mockResolvedValue(
+      ndjsonResponse([startEvent(3), chunkEvent(0), { type: 'error', detail: 'boom' }]),
+    );
+    await expect(streamGenerateSpeech(new FormData(), {})).rejects.toMatchObject({
+      errorClass: null,
+    });
+  });
+
   it('carries the retryable marker from a GPU-timeout error frame (#1190)', async () => {
     // A retryable failure means the backend already spent the full budget on
     // this text and the abandoned job still holds the device — useTTS uses
diff --git a/frontend/src/utils/bugReport.js b/frontend/src/utils/bugReport.js
index 1251cc84..058ea49b 100644
--- a/frontend/src/utils/bugReport.js
+++ b/frontend/src/utils/bugReport.js
@@ -362,11 +362,16 @@ export async function buildBugReportUrl({ title = '[Bug] ', error } = {}) {
       msg.length > MAX_MSG_CHARS ? `${msg.slice(0, MAX_MSG_CHARS)}\n… (truncated)` : msg;
     let stack = error?.stack ? scrubText(error.stack) : '';
     if (stack.length > MAX_STACK_CHARS) stack = `${stack.slice(0, MAX_STACK_CHARS)}\n… (truncated)`;
+    // A generic failure message plus a stack of minified bundle frames is
+    // the same report every time; the backend class name is what separates
+    // one unclassified engine failure from another (#1800).
+    const klass = typeof error?.errorClass === 'string' ? scrubText(error.errorClass) : '';
     errorSection.push(
       '## Error',
       '',
       '```',
       msgForBody,
+      ...(klass ? [`Backend error class: ${klass}`] : []),
       ...(stack && stack !== msgForBody ? [stack] : []),
       '```',
       '',
diff --git a/frontend/src/utils/bugReport.test.js b/frontend/src/utils/bugReport.test.js
index 96246b0a..209d2b90 100644
--- a/frontend/src/utils/bugReport.test.js
+++ b/frontend/src/utils/bugReport.test.js
@@ -117,6 +117,18 @@ describe('buildBugReportUrl', () => {
     expect(body).not.toContain('/Users/alice');
   });
 
+  it('records the backend error class so identical messages differ (#1800)', async () => {
+    const err = new Error('Generation failed. Check the selected engine and try again.');
+    err.errorClass = 'MemoryError';
+    const body = decodeURIComponent(await buildBugReportUrl({ error: err }));
+    expect(body).toContain('Backend error class: MemoryError');
+  });
+
+  it('omits the class line when the failure carries none', async () => {
+    const body = decodeURIComponent(await buildBugReportUrl({ error: new Error('plain failure') }));
+    expect(body).not.toContain('Backend error class');
+  });
+
   it('seeds the title with the error message', async () => {
     const url = await buildBugReportUrl({ error: new Error('synthesis exploded') });
     expect(decodeURIComponent(url)).toContain('[Bug] synthesis exploded');
diff --git a/frontend/src/utils/streamingTts.js b/frontend/src/utils/streamingTts.js
index 7f0d6da7..832df5ae 100644
--- a/frontend/src/utils/streamingTts.js
+++ b/frontend/src/utils/streamingTts.js
@@ -80,6 +80,11 @@ export class StreamingPreviewError extends Error {
     this.retryable = opts?.retryable === true;
     this.retryAfter = opts?.retryAfter ?? null;
     this.terminal = opts?.terminal === true;
+    // The backend exception TYPE behind an otherwise generic failure. The
+    // floor message is identical for every unclassified engine failure, so
+    // without this an auto-filed report cannot be told apart from any
+    // other (#1800). Never the exception message — only its class name.
+    this.errorClass = opts?.errorClass || null;
   }
 }
 
@@ -404,6 +409,7 @@ async function _streamGenerateSpeech(
           retryable: ev.retryable === true,
           retryAfter: ev.retry_after ?? null,
           terminal,
+          errorClass: ev.error_class || null,
         });
       }
     };
diff --git a/tests/backend/core/test_parent_liveness.py b/tests/backend/core/test_parent_liveness.py
index f33eeb2c..343a6f3f 100644
--- a/tests/backend/core/test_parent_liveness.py
+++ b/tests/backend/core/test_parent_liveness.py
@@ -4,6 +4,8 @@ import subprocess
 import sys
 from pathlib import Path
 
+import pytest
+
 def test_parent_pipe_eof_exits_cleanly():
     from core.parent_liveness import _watch_parent_pipe
 
@@ -53,3 +55,207 @@ def test_desktop_child_exits_when_parent_closes_stdin():
         if child.poll() is None:
             child.kill()
             child.wait()
+
+
+# ── Windows: the watchdog must never leave a read pending on the stdin pipe ──
+# A synchronous ReadFile parked on the desktop-owned stdin pipe (via the C
+# runtime's read() or straight to the kernel) deadlocked the OpenBLAS DLL
+# initializer that `import torch` reaches in the startup worker: every
+# desktop-spawned backend on Windows froze at "Loading ML runtime" while the
+# same command from a terminal (no stdin pipe, no watchdog) started in seconds.
+# A thread that only sleeps is harmless; the pending read is the trigger. The
+# Windows watcher therefore polls PeekNamedPipe and reads only bytes that are
+# already buffered, so no I/O is ever outstanding on that file object.
+
+
+def _peek_sequence(events):
+    """`events` items: int → bytes available; OSError → broken pipe."""
+    it = iter(events)
+
+    def peek(handle):
+        ev = next(it)
+        if isinstance(ev, BaseException):
+            raise ev
+        return (ev, 0)
+
+    return peek
+
+
+def test_windows_watcher_exits_on_broken_pipe_without_blocking_reads():
+    from core.parent_liveness import _watch_parent_pipe_handle
+
+    reads, sleeps, exits = [], [], []
+    _watch_parent_pipe_handle(
+        7,
+        exits.append,
+        peek=_peek_sequence([0, 0, OSError(109, "The pipe has been ended")]),
+        read_file=lambda h, n: reads.append((h, n)),
+        sleep=sleeps.append,
+        interval=0.01,
+    )
+    assert exits == [0]
+    assert reads == []  # nothing buffered → never a read, let alone a pending one
+    assert sleeps == [0.01, 0.01]
+
+
+def test_windows_watcher_drains_only_buffered_bytes_until_eof():
+    from core.parent_liveness import _watch_parent_pipe_handle
+
+    reads, exits = [], []
+    _watch_parent_pipe_handle(
+        7,
+        exits.append,
+        peek=_peek_sequence([3, 0, 1, OSError(109, "The pipe has been ended")]),
+        read_file=lambda h, n: reads.append((h, n)) or (b"x" * n, 0),
+        sleep=lambda s: None,
+    )
+    assert exits == [0]
+    # Reads are sized to exactly what PeekNamedPipe reported, so they return
+    # immediately instead of parking on the pipe.
+    assert reads == [(7, 3), (7, 1)]
+
+
+def test_windows_watchdog_arms_pipe_poller_on_pipe_stdin(monkeypatch):
+    import types
+    import core.parent_liveness as pl
+
+    monkeypatch.setenv("OMNIVOICE_DESKTOP_CONTAINED", "1")
+    monkeypatch.setattr(pl.os, "name", "nt")
+
+    class FakeBuffer:
+        def fileno(self):
+            return 0
+
+    monkeypatch.setattr(pl.sys, "stdin", types.SimpleNamespace(buffer=FakeBuffer()))
+    monkeypatch.setitem(sys.modules, "msvcrt", types.SimpleNamespace(get_osfhandle=lambda fd: 0xABC))
+    monkeypatch.setitem(sys.modules, "_winapi", types.SimpleNamespace(GetFileType=lambda h: 3))
+
+    started = {}
+
+    class FakeThread:
+        def __init__(self, *, target, args, name, daemon):
+            started.update(target=target, args=args, daemon=daemon)
+
+        def start(self):
+            started["started"] = True
+
+    monkeypatch.setattr(pl.threading, "Thread", FakeThread)
+    assert pl.arm_desktop_parent_watchdog() is True
+    assert started["started"] is True
+    assert started["target"] is pl._watch_parent_pipe_handle
+    assert started["args"] == (0xABC, os._exit)
+    assert started["daemon"] is True
+
+
+def test_windows_watchdog_keeps_blocking_reader_for_non_pipe_stdin(monkeypatch):
+    """A file/NUL stdin has no pipe file object to deadlock against, and a
+    blocking read on it returns EOF promptly — keep the shared reader there."""
+    import types
+    import core.parent_liveness as pl
+
+    monkeypatch.setenv("OMNIVOICE_DESKTOP_CONTAINED", "1")
+    monkeypatch.setattr(pl.os, "name", "nt")
+
+    class FakeBuffer:
+        def fileno(self):
+            return 0
+
+    fake_stdin = types.SimpleNamespace(buffer=FakeBuffer())
+    monkeypatch.setattr(pl.sys, "stdin", fake_stdin)
+    monkeypatch.setitem(sys.modules, "msvcrt", types.SimpleNamespace(get_osfhandle=lambda fd: 0xABC))
+    monkeypatch.setitem(sys.modules, "_winapi", types.SimpleNamespace(GetFileType=lambda h: 1))  # FILE_TYPE_DISK
+
+    started = {}
+
+    class FakeThread:
+        def __init__(self, *, target, args, name, daemon):
+            started.update(target=target, args=args)
+
+        def start(self):
+            started["started"] = True
+
+    monkeypatch.setattr(pl.threading, "Thread", FakeThread)
+    assert pl.arm_desktop_parent_watchdog() is True
+    assert started["target"] is pl._watch_parent_pipe
+    assert started["args"] == (fake_stdin.buffer, os._exit)
+
+
+# ── Windows integration: the real backend must get past the ML import ────────
+# The deadlock needs the real startup: numpy's OpenBLAS DLL loaded through
+# `import torch` in the startup worker while the desktop watchdog is armed on a
+# piped stdin. Smaller reproductions (a pending read + `import torch` in a bare
+# child) do not trigger it, so this spawns the actual backend exactly as the
+# desktop shell does. It fails on the pre-fix watchdog by timing out in the
+# "ml_imports" step and passes in well under a minute on the fix. Windows-only:
+# CI's backend job runs on Linux, so this is exercised on Windows dev machines.
+
+
+@pytest.mark.skipif(sys.platform != "win32", reason="desktop stdin-pipe watchdog deadlock is Windows-only")
+def test_desktop_spawned_backend_gets_past_ml_imports_on_windows(tmp_path):
+    pytest.importorskip("torch")
+    pytest.importorskip("uvicorn")
+    import json
+    import socket
+    import threading
+    import time
+    import urllib.request
+
+    with socket.socket() as probe:
+        probe.bind(("127.0.0.1", 0))
+        port = probe.getsockname()[1]
+
+    root = Path(__file__).parents[3]
+    env = os.environ.copy()
+    env.update(
+        {
+            "OMNIVOICE_DESKTOP_CONTAINED": "1",  # arms the watchdog on the stdin pipe
+            "OMNIVOICE_PORT": str(port),
+            "OMNIVOICE_DATA_DIR": str(tmp_path / "data"),
+            "OMNIVOICE_CACHE_DIR": str(tmp_path / "hf_cache"),
+            "HF_HUB_CACHE": str(tmp_path / "hf_cache"),  # never the developer's populated cache
+            "HF_HUB_OFFLINE": "1",
+            "PYTHONUNBUFFERED": "1",
+            "PYTHONUTF8": "1",
+        }
+    )
+    env.pop("PYTHONPATH", None)
+    child = subprocess.Popen(
+        [sys.executable, "-m", "uvicorn", "main:app", "--app-dir", "backend",
+         "--host", "127.0.0.1", "--port", str(port)],
+        cwd=root,
+        env=env,
+        stdin=subprocess.PIPE,   # the desktop shell keeps this open and never writes
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+    for stream in (child.stdout, child.stderr):
+        threading.Thread(target=lambda s=stream: s.read(), daemon=True).start()
+    seen = []
+    try:
+        deadline = time.time() + 180
+        while time.time() < deadline:
+            if child.poll() is not None:
+                pytest.fail(f"backend exited early with {child.returncode}; progress seen: {seen[-3:]}")
+            try:
+                with urllib.request.urlopen(f"http://127.0.0.1:{port}/startup/progress", timeout=2) as resp:
+                    progress = json.load(resp)
+            except (OSError, ValueError):
+                time.sleep(1)
+                continue
+            status = progress.get("status")
+            seen.append((status, progress.get("step")))
+            done = {s["id"] for s in progress.get("steps", []) if s.get("state") == "done"}
+            # Positive evidence only: the ML import step finished, or startup is
+            # ready. Any other terminal state is the failure this test exists for.
+            if "ml_imports" in done or status == "ready":
+                return
+            if status != "starting" or progress.get("error"):
+                pytest.fail(
+                    f"backend startup reported status={status!r} error={progress.get('error')!r}; "
+                    f"progress seen: {seen[-3:]}"
+                )
+            time.sleep(1)
+        pytest.fail(f"backend never got past ml_imports in 180s (deadlocked watchdog?); last progress: {seen[-3:]}")
+    finally:
+        child.kill()
+        child.wait()
diff --git a/tests/test_context_free_hints_1943.py b/tests/test_context_free_hints_1943.py
new file mode 100644
index 00000000..967a06d6
--- /dev/null
+++ b/tests/test_context_free_hints_1943.py
@@ -0,0 +1,69 @@
+"""#1943 — a context-free surface must not attach a stage-specific hint.
+
+A macOS mlx-audio text-to-speech failure came back as a 500 reading "… The
+connection to the video server dropped mid-download (often a transient
+CDN/network blip …)". No video was involved. VIDEO_DOWNLOAD_NETWORK triggers
+on bare phrases like "timed out" and "connection reset", so any unrelated
+failure whose message contains one is handed a confidently wrong remediation.
+
+failure._CONTEXT_FREE_HINT_CLASSES already existed for this, and its own
+comment names VIDEO_DOWNLOAD_NETWORK as the class that must never appear on a
+context-free surface. Only append_hint honoured it; public_exception_response
+replaced append_hint on the 500 path without carrying the rule across.
+"""
+import pytest
+
+from core.failure import _CONTEXT_FREE_HINT_CLASSES, classify
+from core.public_errors import public_exception_response, stream_generation_failure
+
+# Phrases that really do classify as the video-download class but say nothing
+# about a video when they arrive from a model load or a synthesis run.
+_GENERIC_NETWORK_WORDING = [
+    "operation timed out",
+    "connection reset by peer",
+    "broken pipe",
+    "remote end closed connection without response",
+]
+
+
+@pytest.mark.parametrize("message", _GENERIC_NETWORK_WORDING)
+def test_no_video_hint_on_a_context_free_failure(message):
+    assert classify(message) == "VIDEO_DOWNLOAD_NETWORK"  # still classified...
+    payload = public_exception_response(RuntimeError(message), fallback="Internal error.")
+    # ...but its hint must not reach a surface that does not know the stage.
+    assert payload["detail"] == "Internal error."
+    assert "video server" not in payload["detail"]
+    assert "docs_topic" not in payload
+
+
+@pytest.mark.parametrize("message", _GENERIC_NETWORK_WORDING)
+def test_no_video_hint_on_the_streaming_generate_frame(message):
+    payload = stream_generation_failure(RuntimeError(message))
+    assert "video" not in str(payload["detail"]).lower()
+    assert "docs_topic" not in payload
+
+
+def test_allowlisted_classes_keep_their_hint():
+    payload = public_exception_response(
+        RuntimeError("CUDA out of memory. Tried to allocate 2.00 GiB"),
+        fallback="Internal error.",
+    )
+    assert payload.get("docs_topic") == "GPU_OOM"
+    assert payload["detail"] != "Internal error."
+
+
+def test_windows_paging_file_keeps_its_hint():
+    # An allowlisted class whose trigger is unmistakable — the regression guard
+    # for over-filtering, which would silently strip every useful remediation.
+    payload = public_exception_response(
+        OSError("[WinError 1455] The paging file is too small for this operation to complete"),
+        fallback="Internal error.",
+    )
+    assert payload.get("docs_topic") == "WINDOWS_PAGING_FILE_TOO_SMALL"
+
+
+def test_the_filter_matches_the_documented_allowlist():
+    # Pins the contract itself: the class the allowlist's own comment calls out
+    # as unsafe must not be a member.
+    assert "VIDEO_DOWNLOAD_NETWORK" not in _CONTEXT_FREE_HINT_CLASSES
+    assert "GPU_OOM" in _CONTEXT_FREE_HINT_CLASSES
diff --git a/tests/test_stream_error_class_1800.py b/tests/test_stream_error_class_1800.py
new file mode 100644
index 00000000..1e35023b
--- /dev/null
+++ b/tests/test_stream_error_class_1800.py
@@ -0,0 +1,53 @@
+"""#1800 — an unclassified streaming failure must carry its exception class.
+
+Every engine failure the taxonomy cannot classify renders the same floor
+message, "Generation failed. Check the selected engine and try again." The
+auto bug reporter puts that message and a stack of minified bundle frames into
+the issue, so roughly a dozen separate faults arrived as byte-identical,
+untriageable reports. The exception's TYPE NAME is what separates them.
+
+It is the type name only. No substring of the exception message is copied, so
+the response-safety contract in tests/test_response_safety.py still holds.
+"""
+import pytest
+
+from core.public_errors import stream_failure, stream_generation_failure
+
+
+def test_unclassified_failure_carries_its_exception_class():
+    payload = stream_generation_failure(RuntimeError("CUDA error: device-side assert"))
+    assert payload["code"] == "generation_failed"
+    assert payload["error_class"] == "RuntimeError"
+
+
+def test_two_unrelated_failures_are_distinguishable():
+    # The whole point: these used to be the same report.
+    a = stream_generation_failure(RuntimeError("boom"))
+    b = stream_generation_failure(MemoryError("out of memory"))
+    assert a["detail"] == b["detail"]
+    assert a["error_class"] != b["error_class"]
+
+
+def test_the_exception_message_is_never_copied():
+    secret = "C:/Users/someone/private-voice-sample.wav"
+    payload = stream_generation_failure(FileNotFoundError(secret))
+    assert payload["error_class"] == "FileNotFoundError"
+    for value in payload.values():
+        assert secret not in str(value)
+        assert "someone" not in str(value)
+
+
+def test_a_non_exception_gets_no_class():
+    # dict(...) of the plain floor payload, unchanged — nothing to name.
+    payload = stream_generation_failure("not an exception")
+    assert "error_class" not in payload
+    assert payload["detail"] == stream_failure("generation_failed")["detail"]
+
+
+@pytest.mark.parametrize("exc", [RuntimeError("x"), ValueError("y"), OSError("z")])
+def test_class_is_present_alongside_a_classified_hint(exc):
+    # Enrichment and the class name are independent: adding one must not drop
+    # the other, whichever branch the taxonomy takes.
+    payload = stream_generation_failure(exc)
+    assert payload["error_class"] == type(exc).__name__
+    assert payload["detail"]