Fix what the last round of device fixes broke, and two dips it missed

A review of d60ed60 and 8b9b936 found five things. Three were introduced by
those commits.

REFUSING A NAMED DEVICE MADE A MARKER PC CLAIM ITS OPERATION. _sync_partmarker
returned [] both for "not a marker PC" and for "a marker PC that linked
nothing", and the caller reads [] as the first - so a bay whose asset-id.txt
named something unresolvable fell through to the ordinary machine link, and for
a marker PC the machine number IS the operation. It took an active link to a
record that can only have one holder while several markers share it, and the
warning said "not linked". The previous behaviour minted a twin; this traded
that for a contested operation. None now means "not a marker PC" and is the only
answer that lets the machine link run; the response normalises it away so the
API shape is unchanged.

A DORMANT CHALLENGER WAS PROMOTED BY DELETING A FILE. Recording a challenger
dormant leaves a row that the next cycle finds as `reuse` and reactivated with
no incumbent check - so a second PC took a live device by its enrollment file
becoming unreadable. Both reuse branches re-check incumbency now, which is what
_sync_machine_link always did.

AN INCUMBENT UNDER ANOTHER COLLECTOR LABEL WAS INVISIBLE. Incumbency was queried
on our own label, but on a CMM the instrument IS the reported bay, so the
incumbent's link is the machine sync's row. A second PC naming that instrument
found no incumbent and linked actively: two live holders of one instrument, each
invisible to the other. Incumbency now counts any collector-owned label. A row
made BY HAND carries none of them and is still excluded - a person's link is not
the collector's to archive.

THE NETWORK FORM LOCKED OUT THE ROWS IT NEEDED TO FIX. Asset number is disabled
while editing, correctly, but the payload is built in script so the blank was
still sent - and the new server-side guard rejects it. A device with no asset
number could not be saved at all, and the field could not be typed into. It now
unlocks only for a record that loaded without one, with a hint saying why.

"2 in 4.0d" WAS THE LABEL LYING. Replacements are counted across the whole
history window; basisdays is only how long the current cartridge has been in.
Joining them with "in" claimed two changes inside four days - the exact shape
reported as unbelievable, except here the data was right. Now "2, this one 4.0d".

Two toner dips the same review found:

A MULTI-POLL OUTAGE STILL MINTED A PHANTOM SWAP. Only single readings were
dropped, so 90, 0, 0, 90 survived and 0 -> 90 scored as a change. Dips of any
length are handled now. One bad sample stays a candidate whatever the polling
cadence, because a reading is an instant; several consecutive low ones only
count as one outage when they are close together, since days at zero is a real
empty period. That time bound also separates an outage from a swap, ordinary
consumption, and a second swap, which have the same shape in levels alone.

THE DIP FILTER ATE REAL SWAPS OF NEARLY-FULL CARTRIDGES. Recovery was tested
with an absolute difference, so 95 then 5 then 100 read as a recovery because
100 and 95 are close, and the swap evidence was deleted. Toner only falls: a
recovery comes back at or BELOW where it left, a new cartridge comes back
higher.

The review also proved by reverting each feature that the previous tests did not
pin the median burn rate or the near-full rule - both passed with the bug
restored. Verified by the same method that all four toner behaviours now fail
when reverted, and the burst assertion is tight enough to tell 0.2 from 0.88.

plugins/tools/frontend/labelPages.spec.js

@@ -0,0 +1,113 @@
+// Page order is the one thing here that costs money to get wrong: a run of
+// badge cards with the backs one card out looks perfect until someone reads
+// one. These tests pin the order and the CSV contract.
+
+import { describe, it, expect } from 'vitest'
+
+import { parseCsv, splitCsvLine, buildPages, MAX_LABELS } from './labelPages'
+
+const sides = pages => pages.map(page => page.side).join(' ')
+const contents = pages => pages.map(page => page.content || '-').join(' ')
+
+describe('splitCsvLine', () => {
+  it('keeps a comma that is inside quotes', () => {
+    expect(splitCsvLine('WJ-0001,"Bay 12, press",2')).toEqual(['WJ-0001', 'Bay 12, press', '2'])
+  })
+
+  it('unescapes a doubled quote', () => {
+    expect(splitCsvLine('x,"the ""big"" one"')).toEqual(['x', 'the "big" one'])
+  })
+})
+
+describe('parseCsv', () => {
+  it('reads a named header in any column order', () => {
+    const rows = parseCsv('copies,label,content\n3,Line 1,WJ-0001')
+    expect(rows).toEqual([
+      { content: 'WJ-0001', label: 'Line 1', copies: 3, back: '', backlabel: '' },
+    ])
+  })
+
+  it('falls back to positional columns with no header', () => {
+    const rows = parseCsv('WJ-0001,Line 1,2,WJ-0001-B,Reverse')
+    expect(rows[0]).toEqual({
+      content: 'WJ-0001', label: 'Line 1', copies: 2,
+      back: 'WJ-0001-B', backlabel: 'Reverse',
+    })
+  })
+
+  it('skips a row with no content rather than printing a blank sticker', () => {
+    expect(parseCsv('content,label\n,orphan\nWJ-0002,real')).toHaveLength(1)
+  })
+
+  it('defaults copies to 1 when it is missing or junk', () => {
+    expect(parseCsv('content,copies\nA,\nB,zero')[0].copies).toBe(1)
+    expect(parseCsv('content,copies\nA,\nB,zero')[1].copies).toBe(1)
+  })
+})
+
+describe('buildPages without a back side', () => {
+  it('expands copies and emits fronts only', () => {
+    const { pages, backs } = buildPages([{ content: 'A', label: 'a', copies: 3 }])
+    expect(sides(pages)).toBe('front front front')
+    expect(backs).toHaveLength(0)
+  })
+
+  it('caps cards, not pages, and says how many it dropped', () => {
+    const { fronts, dropped } = buildPages([{ content: 'A', copies: MAX_LABELS + 5 }])
+    expect(fronts).toHaveLength(MAX_LABELS)
+    expect(dropped).toBe(5)
+  })
+})
+
+describe('buildPages with a back side', () => {
+  const rows = [
+    { content: 'A', label: 'a', copies: 2, back: 'A2', backlabel: 'a2' },
+    { content: 'B', label: 'b', copies: 1, back: 'B2', backlabel: 'b2' },
+  ]
+
+  it('interleaves front and back, which is what a duplex driver takes', () => {
+    const { pages } = buildPages(rows, { back: { enabled: true, source: 'column', order: 'interleave' } })
+    expect(sides(pages)).toBe('front back front back front back')
+    expect(contents(pages)).toBe('A A2 A A2 B B2')
+  })
+
+  it('groups every front then every back, for a flip-and-reload printer', () => {
+    const { pages } = buildPages(rows, { back: { enabled: true, source: 'column', order: 'grouped' } })
+    expect(sides(pages)).toBe('front front front back back back')
+    // Same card order in both halves, or the flipped stack pairs up wrong.
+    expect(contents(pages)).toBe('A A B A2 A2 B2')
+  })
+
+  it('still emits a back for a row that left the back column empty', () => {
+    const { pages } = buildPages(
+      [{ content: 'A', copies: 1 }, { content: 'B', copies: 1, back: 'B2' }],
+      { back: { enabled: true, source: 'column', order: 'interleave' } })
+    // A page count that changes per row would shift every later back onto the
+    // wrong front.
+    expect(sides(pages)).toBe('front back front back')
+    expect(contents(pages)).toBe('A - B B2')
+  })
+
+  it('repeats the front payload when the back is the same code', () => {
+    const { backs } = buildPages(rows, { back: { enabled: true, source: 'code' } })
+    expect(contents(backs)).toBe('A A B')
+  })
+
+  it('puts the same fixed text on every back and no code', () => {
+    const { backs } = buildPages(rows, { back: { enabled: true, source: 'text', text: 'Property of GE' } })
+    expect(backs.every(page => page.content === '')).toBe(true)
+    expect(backs.every(page => page.label === 'Property of GE')).toBe(true)
+  })
+
+  it('leaves a blank back entirely empty but still counted', () => {
+    const { pages, backs } = buildPages(rows, { back: { enabled: true, source: 'blank' } })
+    expect(pages).toHaveLength(6)
+    expect(backs.every(page => !page.content && !page.label)).toBe(true)
+  })
+
+  it('falls back to the fixed text when a row has no back label', () => {
+    const { backs } = buildPages([{ content: 'A', copies: 1, back: 'A2' }],
+      { back: { enabled: true, source: 'column', text: 'Return to IT' } })
+    expect(backs[0].label).toBe('Return to IT')
+  })
+})