fix(pad): restore Accept-Language auto-detect on pad UI (#7586)

[JohnMcLear]

Summary

Fixes #7586. In v2.7.0 the pad UI stopped honouring the browser's Accept-Language / locale, always rendering English regardless of system language. The index page and the timeslider were unaffected; only the pad route regressed.

Root cause

The regression was introduced by #7545 ("Add creator-owned pad settings defaults"), which added this line to Pad.normalizePadSettings():

lang: typeof rawPadSettings.lang === 'string' ? rawPadSettings.lang : 'en',

That default propagates into clientVars.padOptions.lang. On the client, getParams() in src/static/js/pad.ts reads padOptions.lang and fires the per-setting callback, which is html10n.localize([val, 'en']). So every pad forced English at load time, defeating the existing auto-detect chain in src/static/js/l10n.ts:

html10n.localize([regexpLang, navigator.language, 'en']);

Fix

Default lang to null instead of 'en'. The client-side flow already handles null correctly — getParams() at pad.ts:172 short-circuits with if (serverValue == null) continue;, so the forced-localize callback simply doesn't fire, and l10n.ts's browser-language chain takes over. The pad-settings dropdown consumer at pad.ts:489 already uses padOptions.lang || 'en' so it renders 'en' visually when no override is set, matching prior behaviour.

PadSettings.lang is widened from string to string | null to match.

Creator override (explicit rawPadSettings.lang = 'de') continues to work — that's still a string, so it's preserved verbatim.

Tests

Added three backend regression tests under normalizePadSettings lang in tests/backend/specs/Pad.ts:

• defaults to null when lang is absent (so client auto-detects)
• preserves an explicit string lang (creator override still works)
• drops non-string lang values to null rather than coercing to 'en'

Test plan

• mocha tests/backend/specs/Pad.ts — 23 passing
• Full backend suite — 802 passing, 0 failing (+3 from this PR)
• tsc --noEmit clean in our code
• Manual: Firefox with German locale → fresh pad renders in German. Index and timeslider unchanged. ?lang=de URL param and language cookie continue to override browser detection.

🤖 Generated with Claude Code

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Review Summary by Qodo

Restore Accept-Language auto-detect on pad UI

🐞 Bug fix 🧪 Tests

Walkthroughs

Description

• Restore browser locale auto-detection on pad UI by defaulting lang to null
• Prevent hardcoded English from overriding Accept-Language and cookie settings
• Add three regression tests for normalizePadSettings lang handling
• Widen PadSettings.lang type to string | null for proper null handling

Diagram

flowchart LR
  A["Pad.normalizePadSettings()"] -->|"lang default changed"| B["lang: null instead of 'en'"]
  B -->|"client-side flow"| C["getParams() skips callback"]
  C -->|"l10n auto-detect runs"| D["cookie → navigator.language → 'en'"]
  E["Creator override lang='de'"] -->|"preserved as string"| F["Works as before"]

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File Changes

1. src/node/db/Pad.ts 🐞 Bug fix +6/-2

Change lang default from 'en' to null

• Changed PadSettings.lang type from string to string | null
• Modified normalizePadSettings() to default lang to null instead of 'en'
• Added explanatory comment about the fix for issue #7586
• Preserves explicit string values for creator overrides

src/node/db/Pad.ts

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2. src/tests/backend/specs/Pad.ts 🧪 Tests +19/-0

Add regression tests for lang normalization

• Added test suite for normalizePadSettings lang regression testing
• Test that lang defaults to null when not provided
• Test that explicit string lang values are preserved
• Test that non-string lang values are coerced to null rather than 'en'

src/tests/backend/specs/Pad.ts

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Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

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