ADR-0005 — DM Sans bundled as default font (base64 data URI)

Status: accepted — legacy path for SiS warehouse / local dev Date: 2026-05-31

Context

Legacy SiS (warehouse) has no filesystem access and no external network calls. A custom font cannot be loaded from a CDN or a local path. The font must be self-contained.

Decision

DM Sans variable font (100–900 weights) is bundled in core/assets/fonts/DMSans.woff2 and embedded at runtime as a base64 data URI by setup_page(). This is the DEFAULT_FONT — used automatically unless overridden.

Override: font=AppFont("Syne", "/path/to/Syne.woff2") or font=None to disable.

Consequences

Identical font rendering in local dev and SiS — no CDN dependency, no network call. Font is included in the package distribution. Any app that calls setup_page() gets DM Sans by default with zero configuration.

Container Runtime — preferred path

In Streamlit Container Runtime (Snowflake Workspace), config.toml supports fontFiles natively. The base64 approach is no longer required.

Preferred for Container Runtime apps:

# Generate config.toml once (commit to project)
PALETTES.PYTHIA.to_config_toml(font_files=["static/DMSans.woff2"])

# In each page
setup_page(session, palette=PALETTES.PYTHIA, font=None)

The base64 path (font=DEFAULT_FONT) remains valid for legacy SiS on warehouse and for local dev without a config.toml. See ADR-0006 for the full Container Runtime strategy.