Keep live stats and today’s self-powered % honest when a meter is down

[frahlg]

Accepted text proposal

Follow-up to merged #980 (Bugbot + Codex review on that PR). Same accepted scope: a quiet meter must not be drawn as live zeros.

What changed

• Live stats strip above the chart now matches the Values tiles: configured-but-offline solar/battery/SoC render —, not 0 W / 0.0 %.
• % SELF-POWERED TODAY is computed from energy.today kWh only. Instantaneous load_w still blanks % SELF-POWERED NOW.
• First /api/status is cached raw and replayed when energy-flow-readings.js assigns the mapper, not only when <ftw-energy-flow> upgrades.

Why

#980 stopped the hero and Values tiles from drawing a stale meter as 0 W balanced. Two leftover surfaces still lied:

1. Site-level pv_w / bat_w / bat_soc become 0 once offline drivers are excluded from the live balance. The stats strip fed those zeros.
2. Today’s self-powered share is historical kWh. Gating it on live load_w hid a day that already happened for the whole outage.

Codex also noted the mapper lives in the deferred module graph, so a fast first status could be dropped until the next 2 s poll. Replay now waits for the mapper as well as the custom element.

Not changing: GRID planet Math.abs + “exporting” subtitle. fmtKw would print a minus next to that word, which is the raw sign the hero never shows. Values tiles already keep the signed watt.

Boundaries and safety

• No control, dispatch, or protocol change.
• Live % still requires a known instantaneous load.
• Houses with no battery configured still show SoC as they did before.

Open PRs: #968 touches web/app.js only at renderModeCatalog (planner buttons). This PR edits the live-stats / hero paint path only.

Verification

• node --test web/energy-flow-readings.test.mjs web/dashboard-simplification.test.mjs web/javascript-syntax.test.mjs
• Offline hybrid inverter mock (grid_w/load_w null, pv_w/bat_w/bat_soc 0, driver last-known still present):
  • Flow: GRID/SOLAR/BATTERY — / no data, EV 0 W idle, hub 63% SELF-POWERED TODAY, no live NOW %
  • Live stats: GRID/PV/LOAD/BATTERY/SoC all —
  • Values: SOLAR/GRID/HOME/BATTERY — / no data, EV 0 W charger

Flow hub keeps 63% self-powered today while live watts are unknown
Live stats strip shows dashes not 0 W
Values tiles say no data

Checklist

• The diff implements one accepted scope and does not add follow-on work.
• I checked open pull requests that touch the same files.
• Tests cover the changed behaviour and its failure path.
• A human reviewed every changed web/UI view in a browser, or no UI changed.
• A Changeset is included, or the change is exempt.
• Every commit has a DCO sign-off.

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[cursor]

Approved: Cursor Bugbot completed successfully with no findings that need human review, and no approval policy requires a human. No reviewers were assigned.

  

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[miravoss26]

Fixes two related honesty bugs when a meter/inverter goes offline:

• The live-stats strip (Grid/PV/Battery/SoC tiles) no longer paints a fake 0 W for a configured-but-offline PV or battery — falls back to null/"—" like the Values tiles already do.
• Today's self-powered % no longer blanks out just because the instantaneous meter reading is null. It's derived from already-accumulated kWh, so a quiet meter shouldn't erase a day that already happened.

Also factors the flow-diagram paint into paintEnergyFlow() and caches the raw status (lastFlowStatus) so it can repaint once either the readings mapper module or the <ftw-energy-flow> element finishes upgrading — avoids sitting in the loading skeleton for an extra poll cycle.

Test coverage added for both changes (dashboard-simplification.test.mjs, energy-flow-readings.test.mjs) and existing tests updated to match the refactor. No correctness or security issues from my read.

Safe to merge from my read.