Backend: thread CouchersContext into urls helpers

Replace the implicit reliance on config["BASE_URL"] in couchers.urls with an
explicit context: every base_url-derived helper now takes a CouchersContext as
its first positional arg and builds from a new context.base_url property
(currently just config["BASE_URL"]). This threads context through the servicer,
notification render, email, tasks and postal layers so that a later per-request /
per-recipient BASE_URL override becomes a small change to one property. The
media/console helpers are unchanged as they are not base_url-derived.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: aapeliv

app/backend/src/couchers/context.py

@@ -3,6 +3,7 @@
 import grpc
 
 from couchers import experimentation
+from couchers.config import config
 from couchers.i18n import LocalizationContext
 
 if TYPE_CHECKING:
@@ -180,6 +181,11 @@ def token(self) -> str:
     def localization(self) -> LocalizationContext:
         return self.__localization
 
+    @property
+    def base_url(self) -> str:
+        # Single choke point for the frontend base URL of links built (via couchers.urls) for this context.
+        return cast(str, config["BASE_URL"])
+
     # Feature-flag evaluation methods mirror the OpenFeature evaluation API, evaluating for this
     # context's user. The gating lives in experimentation; we just pass our cached per-request
     # evaluator. The in-code default is honored even for flags not yet set up in GrowthBook.

app/backend/src/couchers/email/calendar_events.py

@@ -6,33 +6,31 @@
 
 from couchers import urls
 from couchers.config import config
+from couchers.context import CouchersContext
 from couchers.email.rendering import get_emails_i18next
-from couchers.i18n import LocalizationContext
 from couchers.proto.internal.jobs_pb2 import EmailAttachment
 from couchers.proto.requests_pb2 import HostRequest
 
 HOST_REQUEST_ICS_FILENAME = "host_request.ics"
 
 
 def create_host_request_attachment(
-    host_request: HostRequest, other_name: str, hosting: bool, loc_context: LocalizationContext
+    host_request: HostRequest, other_name: str, hosting: bool, context: CouchersContext
 ) -> EmailAttachment:
-    ics = create_host_request_ics(host_request, other_name, hosting, loc_context)
+    ics = create_host_request_ics(host_request, other_name, hosting, context)
     return ics_to_attachment(ics, HOST_REQUEST_ICS_FILENAME)
 
 
-def create_host_request_ics(
-    host_request: HostRequest, other_name: str, hosting: bool, loc_context: LocalizationContext
-) -> str:
-    event = create_host_request_event(host_request, other_name, hosting, loc_context)
+def create_host_request_ics(host_request: HostRequest, other_name: str, hosting: bool, context: CouchersContext) -> str:
+    event = create_host_request_event(host_request, other_name, hosting, context)
 
     # METHOD:PUBLISH means this is part of a stream of calendar event information.
     # It allows for later cancellation, and doesn't expose accept/decline functionality.
-    return event_to_ics(event, "PUBLISH", loc_context)
+    return event_to_ics(event, "PUBLISH", context)
 
 
 def create_host_request_event(
-    host_request: HostRequest, other_name: str, hosting: bool, loc_context: LocalizationContext, sequence: int = 0
+    host_request: HostRequest, other_name: str, hosting: bool, context: CouchersContext, sequence: int = 0
 ) -> Event:
     """Creates an ics event for a host request."""
 
@@ -44,11 +42,11 @@ def create_host_request_event(
 
     if hosting:
         event.name = get_emails_i18next().localize(
-            "calendar_events.host_requests.title_host", loc_context.locale, {"name": other_name}
+            "calendar_events.host_requests.title_host", context.localization.locale, {"name": other_name}
         )
     else:
         event.name = get_emails_i18next().localize(
-            "calendar_events.host_requests.title_surfer", loc_context.locale, {"name": other_name}
+            "calendar_events.host_requests.title_surfer", context.localization.locale, {"name": other_name}
         )
 
     # Our to_date is inclusive, iCalendar's DTEND is exclusive (for full-day events)
@@ -58,7 +56,7 @@ def create_host_request_event(
     event.make_all_day()
 
     event.location = host_request.hosting_city
-    event.url = urls.host_request(host_request_id=str(host_request.host_request_id))
+    event.url = urls.host_request(context, host_request_id=str(host_request.host_request_id))
 
     # Google Calendar™ will hide the URL if there is a location, so also include it in the description
     event.description = event.url
@@ -67,30 +65,30 @@ def create_host_request_event(
 
 
 def create_host_request_cancellation_attachment(
-    host_request: HostRequest, other_name: str, hosting: bool, loc_context: LocalizationContext
+    host_request: HostRequest, other_name: str, hosting: bool, context: CouchersContext
 ) -> EmailAttachment:
-    ics = create_host_request_cancellation_ics(host_request, other_name, hosting, loc_context)
+    ics = create_host_request_cancellation_ics(host_request, other_name, hosting, context)
     return ics_to_attachment(ics, HOST_REQUEST_ICS_FILENAME)
 
 
 def create_host_request_cancellation_ics(
-    host_request: HostRequest, other_name: str, hosting: bool, loc_context: LocalizationContext
+    host_request: HostRequest, other_name: str, hosting: bool, context: CouchersContext
 ) -> str:
-    event = create_host_request_event(host_request, other_name, hosting, loc_context, sequence=1)
+    event = create_host_request_event(host_request, other_name, hosting, context, sequence=1)
     event.name = get_emails_i18next().localize(
-        "calendar_events.title_cancelled", loc_context.locale, {"title": event.name}
+        "calendar_events.title_cancelled", context.localization.locale, {"title": event.name}
     )
     event.status = "CANCELLED"
 
     # METHOD:PUBLISH means this is part of a stream of calendar event information.
     # Gmail™ will immediately remove the event from the user's calendar.
     # METHOD:CANCEL might leave the event in cancelled state or not work.
-    return event_to_ics(event, "PUBLISH", loc_context)
+    return event_to_ics(event, "PUBLISH", context)
 
 
-def event_to_ics(event: Event, method: str | None, loc_context: LocalizationContext) -> str:
+def event_to_ics(event: Event, method: str | None, context: CouchersContext) -> str:
     # PRODID is mandatory and generally follows "-//[Organization]//[Product Name]//[Language]"
-    calendar = Calendar(creator=f"-//Couchers.org//Couchers//{loc_context.locale.upper()}")
+    calendar = Calendar(creator=f"-//Couchers.org//Couchers//{context.localization.locale.upper()}")
     if method:
         calendar.method = method
     calendar.events.add(event)

app/backend/src/couchers/email/dump_emails.py

@@ -11,6 +11,7 @@
 from pathlib import Path
 
 import couchers.email.emails
+from couchers.context import CouchersContext, make_logged_out_context
 from couchers.email.emails import EmailBase
 from couchers.email.rendering import (
     EmailFooter,
@@ -43,7 +44,7 @@ def parse(args: list[str]) -> CommandLineArgs:
 
 def main() -> None:
     args = CommandLineArgs.parse(sys.argv[1:])
-    loc_context = LocalizationContext(locale=args.locale, timezone=UTC)
+    context = make_logged_out_context(LocalizationContext(locale=args.locale, timezone=UTC))
 
     footer = EmailFooter(
         timezone_name="UTC",
@@ -59,14 +60,14 @@ def main() -> None:
     for _, klass in inspect.getmembers(couchers.email.emails, lambda o: inspect.isclass(o) and o.__base__ == EmailBase):
         email_class: type[EmailBase] = klass
         if filter_regex.fullmatch(email_class.__name__):
-            dump_email(email_class.dummy_data(), footer, loc_context, args.outdir)
+            dump_email(email_class.dummy_data(), footer, context, args.outdir)
 
 
-def dump_email(email: EmailBase, footer: EmailFooter, loc_context: LocalizationContext, outdir: Path) -> None:
+def dump_email(email: EmailBase, footer: EmailFooter, context: CouchersContext, outdir: Path) -> None:
     """Dumps an email's subject and plaintext+html body to a file."""
-    subject_line = email.get_subject_line(loc_context)
-    preview_line = email.get_preview_line(loc_context)
-    blocks = email.get_body_blocks(loc_context)
+    subject_line = email.get_subject_line(context)
+    preview_line = email.get_preview_line(context)
+    blocks = email.get_body_blocks(context)
 
     outdir.mkdir(exist_ok=True)
 
@@ -76,13 +77,13 @@ def dump_email(email: EmailBase, footer: EmailFooter, loc_context: LocalizationC
     html_path = outdir / f"{email.__class__.__name__}.html"
     print(f"  Rendering html to {html_path}...")
     html = render_html_body(
-        subject=subject_line, preview=preview_line, blocks=blocks, footer=footer, loc_context=loc_context
+        subject=subject_line, preview=preview_line, blocks=blocks, footer=footer, loc_context=context.localization
     )
     html_path.write_text(html)
 
     plaintext_path = outdir / f"{email.__class__.__name__}.txt"
     print(f"  Rendering plaintext to {plaintext_path}...")
-    plaintext = render_plaintext_body(blocks=blocks, footer=footer, loc_context=loc_context)
+    plaintext = render_plaintext_body(blocks=blocks, footer=footer, loc_context=context.localization)
     plaintext_path.write_text(plaintext)