fix(packaging): ship locales/ i18n catalogs in wheel, sdist, and Nix (#38383)

* fix(packaging): ship locales/ i18n catalogs in wheel, sdist, and Nix

locales/ is a bare data dir (no __init__.py), invisible to packages.find
and package-data. Sealed installs (pip wheel, Nix store venv) dropped it,
so gateway/CLI commands rendered raw i18n keys like
gateway.reset.header_default.

- pyproject: [tool.setuptools.data-files] locales = ["locales/*.yaml"] (wheel)
- MANIFEST.in: graft locales (sdist)
- agent/i18n._locales_dir: env override -> source -> sysconfig data scheme
- nix/hermes-agent.nix: copy locales into the store + set HERMES_BUNDLED_LOCALES
  as defense-in-depth. The wheel's data-files already materialize into the
  uv2nix venv, so resolution works with no env var; the override pins the
  store path against a future uv2nix change that could drop data-files.
- tests: metadata regression, wheel + sdist build-install smoke tests, and a
  bundled-locales flake check that verifies BOTH the wrapper override and the
  env-var-less data-files path. Smoke test wired into CI.

Closes #23943, #27632, #35374.
Supersedes #23966, #27716, #30261, #33841, #35429, #35494, #35735, #36697.

* test: cap locale e2e timeout, tighten catalog count guard

The two wheel/sdist e2e tests inherit the global --timeout=30 from
addopts; a cold-CI run (isolated build env + venv create + network pip
install) can plausibly exceed it. Add @pytest.mark.timeout(300) so they
don't ride the unit-test budget and flake intermittently.

Also assert the shipped catalog count equals len(SUPPORTED_LANGUAGES)
instead of a hardcoded >=16 floor, so the guard self-updates and trips
on a single dropped catalog (not just a fully-empty graft).

agent/i18n.py

@@ -32,6 +32,7 @@ from __future__ import annotations
 
 import logging
 import os
+import sysconfig
 import threading
 from functools import lru_cache
 from pathlib import Path
@@ -87,11 +88,54 @@ _catalog_lock = threading.Lock()
 def _locales_dir() -> Path:
     """Return the directory containing locale YAML files.
 
-    Lives next to the repo root so both the bundled install and editable
-    checkouts find it without PYTHONPATH gymnastics.
+    Resolution order, first existing wins:
+
+    1. ``HERMES_BUNDLED_LOCALES`` env var -- set by the Nix wrapper (or any
+       sealed-packaging system) to point at the installed catalog directory.
+    2. ``<repo-root>/locales`` -- source checkouts and ``pip install -e .``,
+       where the working tree sits next to ``agent/``.
+    3. ``<sysconfig data|purelib|platlib>/locales`` -- pip wheel installs.
+       setuptools ``data-files`` extracts ``locales/*.yaml`` under the
+       interpreter's ``data`` scheme; the other schemes are checked as a
+       safety net for nonstandard layouts.
+
+    Falling through to the source-style path (even when missing) keeps
+    ``_load_catalog`` error messages informative -- it logs the path it
+    looked at -- rather than raising.
     """
-    # agent/i18n.py -> agent/ -> repo root
-    return Path(__file__).resolve().parent.parent / "locales"
+    override = os.getenv("HERMES_BUNDLED_LOCALES", "").strip()
+    if override:
+        candidate = Path(override)
+        if candidate.is_dir():
+            return candidate
+        logger.warning(
+            "HERMES_BUNDLED_LOCALES points to a non-directory path (%s); "
+            "falling back to bundled/source locale resolution",
+            override,
+        )
+
+    # agent/i18n.py -> agent/ -> repo root (source checkout, editable install)
+    source_dir = Path(__file__).resolve().parent.parent / "locales"
+    if source_dir.is_dir():
+        return source_dir
+
+    # pip wheel install: data-files lands under the interpreter data scheme.
+    # ``data`` (== sys.prefix in a venv) is where setuptools data-files extract
+    # and is checked first. ``purelib``/``platlib`` (site-packages) are a safety
+    # net for nonstandard layouts. NOTE: this does NOT cover ``pip install
+    # --user`` (user scheme, ~/.local/locales) or ``pip install --target`` --
+    # both are out of scope; see the plan header.
+    for scheme in ("data", "purelib", "platlib"):
+        raw = sysconfig.get_path(scheme)
+        if not raw:
+            continue
+        candidate = Path(raw) / "locales"
+        if candidate.is_dir():
+            return candidate
+
+    # Last resort: return the source-style path so _load_catalog's catalog-missing
+    # log (logger.debug "i18n catalog missing for %s at %s") stays informative.
+    return source_dir
 
 
 def _normalize_lang(value: Any) -> str: