diff --git a/docs/production-runbook.md b/docs/production-runbook.md
index 891e5d1..a77afc1 100644
--- a/docs/production-runbook.md
+++ b/docs/production-runbook.md
@@ -21,7 +21,9 @@ This runbook is the operational checklist for releasing and monitoring the trans
 
 1. Deploy artifact/config to target environment.
    - V6.0 Phase 1 production stack: `docker compose -f docker-compose.production.yml up -d --build`
+   - `Settings` loads from explicit `_env_file`, then `ENV_FILE`, then the repository-root `.env.production`; it does not resolve relative to the process working directory.
    - For Runtime Settings writes in production, mount `.env.production` into the app container and set `RUNTIME_SETTINGS_ENV_FILE=/app/.env.production`.
+   - If deployment uses a non-default env-file location, set both `ENV_FILE` and `RUNTIME_SETTINGS_ENV_FILE` to that absolute path so startup reads and Settings-page writes stay aligned.
    - For SQLite -> PostgreSQL cutover, run `uv run python tools/export_import_migration.py verify --source-db <sqlite-path-or-url> --target-db <postgres-url>` before switching runtime.
 2. Validate service startup:
    - `/healthz` responds `200`
diff --git a/docs/ui/pages/settings.md b/docs/ui/pages/settings.md
index db45f69..8db27f5 100644
--- a/docs/ui/pages/settings.md
+++ b/docs/ui/pages/settings.md
@@ -24,7 +24,8 @@ Settings manages installation-local registries, safe runtime .env settings, and
 - Runtime Settings exposes an allowlisted set of non-secret fields synchronized with `Settings` model fields except excluded secret/unsafe fields.
 - Runtime Settings is rendered as a compact two-column editor (**Setting**, **Value**) in a centered, narrower responsive container.
 - Runtime Settings persists changes to the resolved runtime env file, validates by constructing a `Settings` instance, and reports validation failures through the shared UI error presenter.
-- The write target resolution order is: explicit function override (tests/tools), `RUNTIME_SETTINGS_ENV_FILE` environment variable (deployment override), then `Settings.model_config.env_file` (default `.env.production`).
+- `Settings` resolves its env file in this order: explicit `_env_file`, `ENV_FILE`, then the repository-root `.env.production`.
+- Runtime Settings resolves its write target in this order: explicit function override (tests/tools), `RUNTIME_SETTINGS_ENV_FILE` environment variable (deployment override), `ENV_FILE`, then the repository-root `.env.production`.
 - Runtime Settings changes require application restart to take effect.
 - Runtime Settings renders a host-side restart command (`docker compose -f docker-compose.production.yml up -d --force-recreate app worker`) so operators can apply saved values without granting Docker control to the app container.
 - Runtime Settings includes an explicit "Other settings not shown here" markdown table listing:
diff --git a/src/transcription/config.py b/src/transcription/config.py
index a5cf204..c3ac0c3 100644
--- a/src/transcription/config.py
+++ b/src/transcription/config.py
@@ -7,6 +7,7 @@ are resolved by the provider adapters, not here.
 
 import copy
 import logging.config
+import os
 from collections.abc import Sequence
 from enum import StrEnum
 from functools import cache
@@ -26,6 +27,16 @@ from pydantic_settings import BaseSettings
 from pydantic_settings import SettingsConfigDict
 
 logger = logging.getLogger(__name__)
+PROJECT_ROOT = Path(__file__).resolve().parents[2]
+DEFAULT_ENV_FILE_NAME = ".env.production"
+
+
+def resolve_settings_env_file_path() -> Path:
+    """Resolve the runtime env file independent of the process working directory."""
+    override = os.getenv("ENV_FILE", "").strip()
+    if override:
+        return Path(override)
+    return PROJECT_ROOT / DEFAULT_ENV_FILE_NAME
 
 
 class Provider(StrEnum):
@@ -66,7 +77,7 @@ DatabaseSettings = Annotated[
 
 class Settings(BaseSettings):
     model_config = SettingsConfigDict(
-        env_file=".env.production",
+        env_file=None,
         env_file_encoding="utf-8",
         extra="ignore",
         env_nested_delimiter="__",
@@ -75,6 +86,11 @@ class Settings(BaseSettings):
         frozen=True,
     )
 
+    def __init__(self, /, **values: Any) -> None:
+        if "_env_file" not in values:
+            values["_env_file"] = resolve_settings_env_file_path()
+        super().__init__(**values)
+
     # --- NiceGUI Server ---
     host: str = "0.0.0.0"
     port: int = 8000
diff --git a/src/transcription/errors.py b/src/transcription/errors.py
index b6c0eb1..8faaa23 100644
--- a/src/transcription/errors.py
+++ b/src/transcription/errors.py
@@ -32,6 +32,11 @@ def new_error_id() -> str:
     return uuid4().hex[:8]
 
 
+def exception_detail(exc: BaseException) -> str:
+    """Return internal-only root-cause text for persisted diagnostics."""
+    return f"{type(exc).__name__}: {exc}"
+
+
 class AppError(RuntimeError):
     """Base application error carrying user-safe handling metadata."""
 
@@ -115,7 +120,7 @@ def classify_unexpected_error(exc: Exception, *, operation: str) -> AppError:
         category=ErrorCategory.INTERNAL_UNEXPECTED,
         suggestion="Retry once. If it persists, review logs and report the error reference id.",
         retriable=False,
-        detail=f"{type(exc).__name__}: {exc}",
+        detail=exception_detail(exc),
     )
     logger.error(
         "Unexpected error operation=%s error_id=%s",
diff --git a/src/transcription/services/errors.py b/src/transcription/services/errors.py
index 22fb166..0335ce9 100644
--- a/src/transcription/services/errors.py
+++ b/src/transcription/services/errors.py
@@ -16,6 +16,10 @@ class PromptLoadError(AppError):
     """Raised when prompt artifacts cannot be loaded safely."""
 
 
+class PromptStoreError(PromptLoadError):
+    """Raised when prompt storage validation or persistence fails."""
+
+
 class TranscriptionError(AppError):
     """Raised when transcription execution fails."""
 
diff --git a/src/transcription/services/prompts.py b/src/transcription/services/prompts.py
index 2025c0d..7a8456a 100644
--- a/src/transcription/services/prompts.py
+++ b/src/transcription/services/prompts.py
@@ -9,17 +9,14 @@ from uuid import uuid4
 
 from ..config import Settings
 from ..config import get_settings
-from ..errors import AppError
 from ..errors import ErrorCategory
+from ..errors import exception_detail
+from .errors import PromptStoreError
 
 PROMPT_EXTENSION = ".md"
 BACKUP_SUFFIX = ".bak"
 
 
-class PromptStoreError(AppError):
-    """Raised when prompt storage validation or persistence fails."""
-
-
 @dataclass(frozen=True, slots=True)
 class PromptSummary:
     """Read model for one editable prompt artifact."""
@@ -189,5 +186,5 @@ class PromptStore:
             message,
             category=ErrorCategory.INFRA_PERSISTENT,
             suggestion="Check prompt directory permissions and available disk space, then retry.",
-            detail=f"{type(exc).__name__}: {exc}",
+            detail=exception_detail(exc),
         )
diff --git a/src/transcription/ui/pages/tags_page.py b/src/transcription/ui/pages/tags_page.py
deleted file mode 100644
index 99ef15d..0000000
--- a/src/transcription/ui/pages/tags_page.py
+++ /dev/null
@@ -1,92 +0,0 @@
-"""Tags browse and filter page registration."""
-
-from __future__ import annotations
-
-from nicegui import ui
-
-from transcription.services.documents import DocumentService
-from transcription.ui.components.app_shell import render_navigation_header
-from transcription.ui.components.cards import archival_card
-from transcription.ui.components.error_presenter import run_ui_action
-from transcription.ui.components.primitives import render_empty_state
-from transcription.ui.components.primitives import section_header_row
-from transcription.ui.theme import page_header
-
-from ...db.session import SessionFactoryDep
-
-
-def register_page() -> None:
-    """Register the tags browse/filter route."""
-
-    @ui.page("/tags")
-    async def tags_page(session_factory: SessionFactoryDep) -> None:
-        document_service = DocumentService(session_factory=session_factory)
-        render_navigation_header(current_path="/tags")
-
-        tags_outcome = await run_ui_action(
-            operation="tags.list",
-            title="Tags unavailable",
-            action=document_service.list_tag_summaries,
-        )
-        if not tags_outcome.ok:
-            return
-        tag_summaries = tags_outcome.value or ()
-        tag_labels = [item.label for item in tag_summaries]
-
-        documents_outcome = await run_ui_action(
-            operation="documents.list",
-            title="Documents unavailable",
-            action=document_service.list_documents,
-        )
-        if not documents_outcome.ok:
-            return
-        documents = documents_outcome.value or ()
-
-        with ui.column().classes("w-full max-w-7xl mx-auto p-4 gap-4"):
-            with section_header_row():
-                page_header("Tags", subtitle="Browse documents by tag.")
-
-            if not tag_summaries:
-                with archival_card(extra_classes="p-8 text-center"):
-                    render_empty_state("No tags are configured yet.")
-                return
-
-            selected_tag = (
-                ui.select(tag_labels, label="Filter by tag")
-                .props("outlined clearable use-input")
-                .classes("w-full md:w-96 ui-form-surface")
-            )
-
-            @ui.refreshable
-            def render_groups() -> None:
-                selected = str(selected_tag.value or "").strip()
-                with ui.column().classes("w-full gap-3"):
-                    rendered_any = False
-                    for summary in tag_summaries:
-                        if selected and summary.label != selected:
-                            continue
-                        tagged_documents = [
-                            document
-                            for document in documents
-                            if any(
-                                link.tag_ref is not None and link.tag_ref.id == summary.id
-                                for link in document.document_tags
-                            )
-                        ]
-                        if not tagged_documents:
-                            continue
-                        rendered_any = True
-                        with archival_card(title=f"{summary.label} ({len(tagged_documents)})"):
-                            for document in sorted(tagged_documents, key=lambda item: item.name.casefold()):
-                                ui.button(
-                                    document.name,
-                                    on_click=lambda _=None, doc_id=document.id: ui.navigate.to(f"/documents/{doc_id}"),
-                                    icon="description",
-                                ).props("flat dense no-caps").classes("self-start ui-link-primary text-xs")
-
-                    if not rendered_any:
-                        with archival_card(extra_classes="p-6"):
-                            render_empty_state("No documents match this tag filter.", italic=True)
-
-            selected_tag.on_value_change(lambda _event: render_groups.refresh())
-            render_groups()
diff --git a/src/transcription/ui/runtime_settings_store.py b/src/transcription/ui/runtime_settings_store.py
index 2b4a881..de735dd 100644
--- a/src/transcription/ui/runtime_settings_store.py
+++ b/src/transcription/ui/runtime_settings_store.py
@@ -16,8 +16,10 @@ from pydantic import ValidationError
 
 from transcription.config import Provider
 from transcription.config import Settings
+from transcription.config import resolve_settings_env_file_path
 from transcription.errors import AppError
 from transcription.errors import ErrorCategory
+from transcription.errors import exception_detail
 
 FieldControl = Literal["text", "bool", "select"]
 
@@ -385,13 +387,14 @@ def save_runtime_settings(
             "Runtime settings file is not writable.",
             category=ErrorCategory.INFRA_PERSISTENT,
             suggestion="Verify file path and write permissions, then retry.",
-            detail=f"Failed writing runtime env file {resolved_env_path}: {type(exc).__name__}: {exc}",
+            detail=f"Failed writing runtime env file {resolved_env_path}: {exception_detail(exc)}",
         ) from exc
     refreshed = Settings(_env_file=resolved_env_path, _cli_parse_args=False)
     return read_runtime_settings_snapshot(settings=refreshed, env_file_path=resolved_env_path)
 
 
 def _resolve_env_file_path(*, settings: Settings, env_file_path: Path | None) -> Path:
+    _ = settings
     if env_file_path is not None:
         return env_file_path
 
@@ -399,20 +402,7 @@ def _resolve_env_file_path(*, settings: Settings, env_file_path: Path | None) ->
     if override:
         return Path(override)
 
-    configured = settings.model_config.get("env_file")
-    if configured is None:
-        return Path(".env.production")
-    if isinstance(configured, Path):
-        return Path(configured)
-    if isinstance(configured, str):
-        return Path(configured)
-    if isinstance(configured, (list, tuple)) and configured:
-        first = configured[0]
-        if isinstance(first, Path):
-            return Path(first)
-        if isinstance(first, str):
-            return Path(first)
-    return Path(".env.production")
+    return resolve_settings_env_file_path()
 
 
 def _display_value(value: object) -> str | bool:
@@ -473,7 +463,7 @@ def _read_env_lines(path: Path) -> list[str]:
             "Runtime settings file is unreadable.",
             category=ErrorCategory.INFRA_PERSISTENT,
             suggestion="Verify file path and read permissions, then retry.",
-            detail=f"Failed reading runtime env file {path}: {type(exc).__name__}: {exc}",
+            detail=f"Failed reading runtime env file {path}: {exception_detail(exc)}",
         ) from exc
 
 
@@ -551,7 +541,7 @@ def _write_env_lines_atomic(*, path: Path, lines: list[str]) -> None:
             "Runtime settings file is not writable.",
             category=ErrorCategory.INFRA_PERSISTENT,
             suggestion="Verify file path and write permissions, then retry.",
-            detail=f"Failed writing runtime env file {path}: {type(exc).__name__}: {exc}",
+            detail=f"Failed writing runtime env file {path}: {exception_detail(exc)}",
         ) from exc
     finally:
         if temp_path is not None:
diff --git a/tests/conftest.py b/tests/conftest.py
index af2f5a1..2289fab 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,6 +4,7 @@ Every test gets a fresh in-memory SQLite database so tests are
 isolated, fast, and leave no artifacts on disk.
 """
 
+import os
 from pathlib import Path
 
 import pytest
@@ -28,9 +29,9 @@ from transcription.services.jobs import JobService
 def isolate_settings_from_local_env_files(tmp_path_factory):
     """Point `Settings` at a controlled stub env file instead of a developer one.
 
-    `Settings.model_config` declares `env_file=".env.production"`, resolved against the
-    current working directory, so a repository-root pytest run would otherwise read real
-    deployment values into tests that assert declared defaults.
+    `Settings()` resolves its env file through the shared config seam, so a repository-root
+    pytest run would otherwise read a developer's real `.env.production` into tests that
+    assert declared defaults.
 
     The stub mirrors what `.github/workflows/quality-gate.yml` writes in CI: only
     `OPENROUTER_API_KEY`, which is required and which many tests need `get_settings()` to
@@ -42,12 +43,15 @@ def isolate_settings_from_local_env_files(tmp_path_factory):
     stub = tmp_path_factory.mktemp("settings-env") / ".env.test"
     stub.write_text("OPENROUTER_API_KEY=test-placeholder-not-a-real-key\n", encoding="utf-8")
 
-    original = Settings.model_config.get("env_file")
-    Settings.model_config["env_file"] = str(stub)
+    original = os.environ.get("ENV_FILE")
+    os.environ["ENV_FILE"] = str(stub)
     try:
         yield
     finally:
-        Settings.model_config["env_file"] = original
+        if original is None:
+            os.environ.pop("ENV_FILE", None)
+        else:
+            os.environ["ENV_FILE"] = original
 
 
 @pytest.fixture
diff --git a/tests/services/test_prompt_store.py b/tests/services/test_prompt_store.py
index ab58926..21a1273 100644
--- a/tests/services/test_prompt_store.py
+++ b/tests/services/test_prompt_store.py
@@ -4,6 +4,7 @@ import pytest
 
 from transcription.config import Settings
 from transcription.errors import ErrorCategory
+from transcription.services.errors import PromptLoadError
 from transcription.services.prompts import PromptStore
 from transcription.services.prompts import PromptStoreError
 
@@ -79,6 +80,13 @@ def test_prompt_creation_and_empty_content_are_rejected(prompt_store):
     assert empty.value.category == ErrorCategory.VALIDATION
 
 
+def test_prompt_store_failures_are_catchable_as_prompt_load_errors(prompt_store):
+    store, _ = prompt_store
+
+    with pytest.raises(PromptLoadError):
+        store.read_prompt("missing.md")
+
+
 def test_recovery_requires_a_backup(prompt_store):
     store, _ = prompt_store
 
diff --git a/tests/test_config_isolation.py b/tests/test_config_isolation.py
index 6886e81..91aa691 100644
--- a/tests/test_config_isolation.py
+++ b/tests/test_config_isolation.py
@@ -1,22 +1,12 @@
-"""Suite-wide isolation of `Settings` from developer environment files.
-
-`Settings.model_config` declares `env_file=".env.production"`, resolved relative to the
-current working directory. Running pytest from the repository root therefore loads a real
-developer env file into tests that construct `Settings(...)` directly, and the declared
-field defaults stop being what the suite actually exercises.
-
-That breaks verification in both directions: tests asserting default behavior fail locally
-for environmental reasons, and tests asserting configured behavior can pass locally against
-values that do not exist in CI. The autouse fixture in `conftest.py` neutralizes the class
-level `env_file` so defaults are authoritative; tests that need file loading still pass
-`_env_file=` explicitly, which takes precedence over the class config.
-"""
+"""Suite-wide isolation of `Settings` from developer environment files."""
 
 from __future__ import annotations
 
 from pathlib import Path
 
+import transcription.config as config_module
 from transcription.config import Settings
+from transcription.config import resolve_settings_env_file_path
 
 
 def test_settings_defaults_are_not_overridden_by_a_local_env_file():
@@ -37,3 +27,23 @@ def test_explicit_env_file_still_loads(tmp_path):
     settings = Settings(openrouter_api_key="test-key", _env_file=env_path, _cli_parse_args=False)
 
     assert settings.port == 9123
+
+
+def test_settings_env_file_resolves_from_override_environment_variable(tmp_path, monkeypatch):
+    env_path = tmp_path / "custom.env"
+    env_path.write_text("PORT=9123\n", encoding="utf-8")
+    monkeypatch.setenv("ENV_FILE", str(env_path))
+
+    settings = Settings(openrouter_api_key="test-key", _cli_parse_args=False)
+
+    assert settings.port == 9123
+
+
+def test_settings_default_env_path_is_anchored_to_project_root(tmp_path, monkeypatch):
+    monkeypatch.delenv("ENV_FILE", raising=False)
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setattr(config_module, "PROJECT_ROOT", tmp_path / "project-root")
+
+    resolved = resolve_settings_env_file_path()
+
+    assert resolved == tmp_path / "project-root" / ".env.production"
diff --git a/tests/test_orphan_sweep.py b/tests/test_orphan_sweep.py
index 10c5b9e..a93da0e 100644
--- a/tests/test_orphan_sweep.py
+++ b/tests/test_orphan_sweep.py
@@ -92,10 +92,6 @@ KNOWN_ORPHANS: dict[str, str] = {
         "Public read helper currently unused by runtime flows, but retained as part of "
         "the SourceService API pending endpoint consolidation."
     ),
-    "src/transcription/ui/pages/tags_page.py": (
-        "Retained temporarily as explicitly dead code until the planned route-retirement "
-        "cleanup deletes the stranded module."
-    ),
 }
 
 
diff --git a/tests/ui/test_runtime_settings_store.py b/tests/ui/test_runtime_settings_store.py
index 77281ab..1f5fcbc 100644
--- a/tests/ui/test_runtime_settings_store.py
+++ b/tests/ui/test_runtime_settings_store.py
@@ -107,6 +107,22 @@ def test_runtime_settings_uses_override_env_file(tmp_path: Path, monkeypatch):
     assert "PORT=9001" in target.read_text(encoding="utf-8")
 
 
+def test_runtime_settings_falls_back_to_shared_settings_env_file_override(tmp_path: Path, monkeypatch):
+    settings = _settings_for_runtime_editing(tmp_path)
+    target = tmp_path / "shared.env"
+    target.write_text("OPENROUTER_API_KEY=test-key\nPORT=8000\n", encoding="utf-8")
+    monkeypatch.delenv("RUNTIME_SETTINGS_ENV_FILE", raising=False)
+    monkeypatch.setenv("ENV_FILE", str(target))
+
+    snapshot = save_runtime_settings(
+        settings=settings,
+        updates={"port": "9001"},
+    )
+
+    assert snapshot.env_file_path == target
+    assert "PORT=9001" in target.read_text(encoding="utf-8")
+
+
 def test_save_runtime_settings_surfaces_unreadable_target(tmp_path: Path, monkeypatch):
     settings = _settings_for_runtime_editing(tmp_path)
     env_path = tmp_path / ".env"