feat(msteams): inline Report chart images + Adaptive Card theming — reach display parity with google_chat

[sipemu]

Summary

The MS Teams adapter now has the full interactive round-trip (#155 — Button/Selection/Form → Adaptive Card actions, verified callback, in-place refresh). What remains before it is at full feature parity with google_chat is the one-way display richness: inline chart images and card theming. This is the Teams sibling of #154 (which did the same for google_chat) and is out of scope for #155 by design.

Current state (post-#155)

crates/triton-chat-msteams/src/surface_mapper.rs:

• Component::Report is ignored. The text mapper drops it (Component::Report { .. } => {}) and the card path (render_card_content in lib.rs) only lifts interactive controls + Dashboard. So an agent that emits a rendered chart (e.g. peacock render_report) shows nothing on Teams.
• Dashboard renders as a FactSet only (metric tiles). No chart image. Per architecture.md §8.7 this is arguably the intended native projection for Teams (ColumnSet/FactSet, skip the rasteriser), so the tiles are fine — but a genuinely rendered chart (a Report) still needs an Image element.
• No card theming. By contrast google_chat's CardChrome pulls get_theme (logo, brand colour, header) and brands every card; Teams cards are unbranded.
• No image-serving route. google_chat serves chart PNGs at a signed …/img/{token} route (serve_dashboard_png); msteams' router has only the /<name>/webhook route.

Proposed work

1. Inline Report → Adaptive Card Image.

• Add report_from_result (mirror google_chat) to lift Component::Report { report_id, args }.
• On a reply carrying a Report, dispatch render_report(report_id, args) through the upstream router with the resolved principal (identity + audit symmetry), take the returned PNG, and embed it in the card.
• Teams Adaptive Cards render images by URL, so this needs the hosting story below (a signed …/img/{token} route serving the cached PNG), OR — if small enough — a data: URI Image (verify Teams' size limits before relying on it).

2. Signed image route.

• Add a GET /<name>/img/{token} route that decodes a signed token and returns the cached PNG, mirroring google_chat's serve_dashboard_png (including the RENDER_REPORT_IMG_MARKER distinction between a dashboard-spec token and an upstream-rendered-PNG token, and the replay guard that a button/form token can't be replayed at …/img/).

3. Adaptive Card theming (get_theme → chrome).

• Add a msteams CardChrome analogue: fetch get_theme from the report upstream and apply title/logo/brand colour to the Adaptive Card (card title/Image header, Action.Style: positive or a container style for brand colour — Adaptive Cards don't take arbitrary hex on buttons, so map brand → the closest native affordance).

4. (Optional) Dashboard-as-image.

• If a Dashboard should ever render as a rasterised chart on Teams (rather than the native FactSet), reuse the same …/img/{token} path. Default remains the native FactSet per §8.7 — decide explicitly.

Out of scope

• The interactive round-trip (done in feat(msteams): interactive Adaptive Cards — render Button/Selection/Form as actions + handle the invoke callback (correlation_key round-trip) #155).
• Changing the native Dashboard → FactSet projection (keep it; §8.7).

Acceptance criteria

• A surface with a Report renders an Adaptive Card carrying the upstream-rendered chart image on Teams.
• The chart image is served from a signed …/img/{token} route; a forged/replayed token is rejected.
• get_theme chrome (title/logo/brand) is applied to interactive + report cards; unset theme = today's unbranded rendering.
• Unit + no-mock integration tests: Report → image card shape; the image route round-trip against the real binary + a fake upstream that returns a PNG; a forged image-token rejection.

References

• feat(msteams): interactive Adaptive Cards — render Button/Selection/Form as actions + handle the invoke callback (correlation_key round-trip) #155 — the interactive round-trip (Adaptive Cards render + callback), the sibling that landed first.
• feat(google_chat): render Dashboard surfaces (Cards v2 / chart image) — currently text-only, dashboards are dropped #154 — the equivalent display work for google_chat (Cards v2 / chart image), the template to follow.
• crates/triton-chat-googlechat/src/{surface_mapper.rs,lib.rs} — report_from_result, dashboard_image_url, serve_dashboard_png, RENDER_REPORT_IMG_MARKER, CardChrome/get_theme.
• architecture.md §8.7 — the Teams "native Adaptive Card projection, skip the rasteriser" note.