Extension live-fetch sync path bypasses the storage-quota byte-size guard options.js enforces

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Context

apps/loopover-miner-extension/options.js's manual-paste flow validates a pasted rankedCandidates payload against a byte-size quota before writing to chrome.storage.local (lines 9-24: measures real serialized UTF-8 byte size via TextEncoder, not the UTF-16 .length, per bug #4863 — "an unbounded paste can silently fail to save or leave storage in a partial state").

apps/loopover-miner-extension/background.js's syncRankedCandidatesFromMinerUi (the live-fetch replacement for manual paste, #4859) writes to the same chrome.storage.local keys (rankedCandidates/rankedCandidatesSavedAt, line 121) with no equivalent size check on the fetched candidates array before writing — the exact #4863 failure mode (silent partial save past the 10 MiB QUOTA_BYTES shared-across-keys limit) can still happen via this path, it just was never guarded here.

Requirements

• Apply the same byte-size validation options.js already performs (measuring real UTF-8 byte size via TextEncoder, comparing against the same MAX_RANKED_CANDIDATES_JSON_BYTES constant) to syncRankedCandidatesFromMinerUi's fetched candidates before the chrome.storage.local.set(...) call.
• On an over-quota fetch result, return the module's existing typed { ok: false, error, minerUiUrl } shape (matching every other failure branch in this function) rather than throwing — per this function's own documented "never throws" contract.
• Reuse the existing size-check logic/constant from options.js rather than duplicating the byte-measurement approach with different logic.

Deliverables

• syncRankedCandidatesFromMinerUi validates fetched candidates against the same byte-size quota options.js enforces
• An over-quota result returns { ok: false, ... } instead of writing a partial payload
• Test asserting an oversized live-fetch payload is rejected the same way an oversized pasted payload already is

Test Coverage Requirements

apps/** extension code — check whether this repo's coverage.include covers apps/loopover-miner-extension; if so, 99%+ Codecov patch coverage plus the regression test above; if excluded, the regression test alone suffices.

Expected Outcome

The live-fetch sync path can no longer silently write a partial/corrupted rankedCandidates payload past the shared 10 MiB storage quota — it fails closed with a typed error, matching the manual-paste flow's existing protection.

Links & Resources

apps/loopover-miner-extension/options.js:9-24 — the existing byte-size guard (precedent to reuse). apps/loopover-miner-extension/background.js:107-124 (syncRankedCandidatesFromMinerUi) — the unguarded write path.

[linear-code]

JSO-4764