fix(web): switching the import ceiling on applies the box's last value (#1674)

[frahlg]

Problem

On 17 October 2026 Göran (#1674, v0.147.2-beta.1, Easee Cloud + Pixii, 25 A three-phase) switched on the peak import limit meaning 7,500 W. The box applied 3,000 W at once (log 14:22:24Z: grid 12,823 W, overage 9,823 W) and his car stopped.

The on-box page posted /api/peak_import_ceiling straight away with readLastPeakLimitW(): the last value in that browser's localStorage (ftw-peak-import-ceiling-w, default 5,000). His browser still held 3,000 W from a test the night before. The box is the record, so a tariff limit must not come from browser storage.

Change

• Box. POST /api/peak_import_ceiling also saves peak_import_ceiling_last_w: the new value when it is above 0, otherwise the ceiling that was on before. The second case covers a ceiling set by an older Core, which stored no last value. /api/status serves peak_import_ceiling_last_w: the ceiling while on, the stored one while off, null if none was ever on.
• Page. The localStorage copy is gone. While off, the slider shows the box's last value. Switching on posts that value and shows it as it applies.
• A box that never had a limit on. There is nothing to restore, so switching on opens the slider and posts nothing. The owner picks a value and presses Save. Before, a fresh browser applied 5,000 W at once, which would also have stopped Göran's car.
• A ceiling the box cannot save is not applied. The handler saves first; if that fails it answers 500 and the live ceiling stays as it was, so a restart cannot bring back a different one (Codex review).
• Save looks off when it is off. Save in the Grid dialog looked the same enabled or disabled, which hid the "press Save" state above. One CSS rule, scoped to .slider-group-compact, dims it while disabled. It also dims the grid target's Save while the planner drives.

go/internal/control is untouched; the EV guard changes there run in #1699 and the thermal budget branch.

Overlap

• fix(control): the import ceiling caps each clock hour's mean import (#1674) #1699 rewrites the comment above handleSetPeakImportCeiling, adds two status fields after pv_surplus_absorb_soc_cap, and appends a test to api_peak_limit_test.go. This branch leaves those lines alone and uses its own test file. A trial merge with the head of fix(control): the import ceiling caps each clock hour's mean import (#1674) #1699 (4d993623) has no conflicts.
• ftw-webapp and ftw-app have no control for the ceiling; they only show the plan's ceilingW. The new field is not in contract/registry.yaml. No paired PR is needed.

Evidence

• go/internal/api/api_peak_import_ceiling_test.go: on, off, off again, and a restart on the same state.db keep 7,500 W as the last value. A ceiling of 6,000 W set before this change survives switching off.
• web/peak-import-ceiling.test.mjs runs the real app.js in a VM, with 3,000 in localStorage. Switching on posts 7,500 (the box's value). With no box value it posts nothing until Save. Off posts 0. Against master's app.js, the first two tests fail and post 3,000.
• Browser review on a local box (this branch, the ferroamp simulator as site meter, 25 A × 3) with ftw-peak-import-ceiling-w = 3000 in localStorage:
  • Box with 7,500 W as last value: the Grid dialog shows Off at 7.5 kW. Switching on posted 7,500 and the box reported 7,500. Off then posted 0, and the box kept 7,500 as last value.
  • Fresh box: Off at 5.0 kW, Save dimmed. Switching on posted nothing; the box stayed at 0 and Save lit up. Save then applied the value shown (7.7 kW), and off and on again restored 7,700.
  • No JavaScript errors.
• make verify: green.

A person should still look at the Grid dialog before merge.

🤖 Generated with Claude Code

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-17T15:23:11.420609Z	0925395	Draft marked ready

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