fix(lvgl): stand the displays down while the app is suspended

[genmon]

An overlay claim on a dual-role surface left its own last frame on the glass after it released, under a live app.

What happens

A board suppresses its blit door for the duration of a claim — every board in the fleet with a dual-role surface does this, so the overlay cannot be painted over a frame later. But suppression drops the pixels while LVGL goes on rendering and goes on getting its lv_display_flush_ready. The library believed those areas had reached the panel, so when the claim lifted nothing was dirty: the overlay's frame sat there with only the widgets that happened to change painting over it.

A body that mutates on change rather than rebuilding — the idiom the authoring sheets teach — never repaints the rest at all.

The fix

LvglModule stands its displays down while the app is suspended (a suspended app cannot draw anything new, so nothing is lost) and stands them up on resume, which invalidates each active screen and repaints every pixel the overlay owned. Only for targets this module still owns: before an app's first bind there is nothing to repaint, and a target lgfx claimed is not ours to touch.

To hear about the suspension at all, onAppRunning moves from Driver up to Extension, and Sandbox::notifyAppRunning calls it on every declared extension rather than only the Drivers among them. That is the right home for it: the extension that most needs to know the app stopped is a graphics module, which owns no hardware and so was never a Driver. Existing Driver overrides are untouched — same signature, same slot, so this is source-compatible.

Evidence

Found on an oracle (360×360 round face, dual-role: cfg.systemDisplay and an app surface) and reproduced in that board's wasm sim, where a still app left 129600 of 129600 pixels unrepainted after an agent_status claim released, and 0 with this change. The consumer repo now smokes that on every board with a status surface.

• test_overlay gains one case: a module-less Extension hears the overlay suspension.
• 225 unit tests pass; cppcheck clean.

Version

0.8.6-dev, with docs/changelog.md and docs/api.md updated (the Extension interface table, the Driver "added interface" section, and the suspendApp paragraph, which said drivers receive the hook).

🤖 Generated with Claude Code