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0009 — timeglyph-lens zone & time display conventions

Status: Accepted

Context

The timeglyph-lens overlay renders a decoded instant in a chosen display zone. Two recurring hazards shape how the zone frame is presented:

  • Misreading the frame — the classic forensic error of reading a local-time value as if it were UTC. The display must make the active frame unmistakable.
  • IANA quirks that confuse — the POSIX Etc/GMT±N ids invert the sign (Etc/GMT-8 is UTC+08:00); Etc/* is a bag of duplicate offset aliases, not a geographic region; many zones report a numeric pseudo-abbreviation (-05) that merely repeats the offset; and Local does not say which zone it resolved to.

Decision

Footer zone chip (zone::zone_summary):

  • Always highlighted amber, including UTC, so the active frame is unmistakable at a glance — replacing the earlier calm-vs-loud styling and the ⚠ caution sign, which the amber highlight plus the explicit offset make redundant.
  • Form Label (ABBR = UTC±HH:MM), e.g. Asia/Shanghai (CST = UTC+08:00); when a zone has no letter code, Name (UTC+05:30); UTC and fixed / Etc offset labels stand alone.
  • Local surfaces the resolved system zone: Local (Asia/Shanghai (HKT) = UTC+08:00).

Zone identifiers:

  • Numeric pseudo-abbreviations (-05) are suppressed (tzinfo::stamp) — they only repeat the offset.
  • Etc/GMT±N ids are relabeled to their true, sign-corrected offset (zone::clean_label: Etc/GMT-8 → UTC+08:00); all Etc/* UTC aliases → UTC.
  • The Etc region stays in the picker but is shown as etc. (zone::continent_label), and every region's submenu is deduplicated and offset-sorted (zone::menu_entries), so Etc reads UTC-12:00 → UTC+14:00 with a single UTC entry instead of the lexical Etc/GMT+1, +10, +11… mess. SystemV (aliases clean_label does not tidy) is excluded.

Readings (overlay::datetime_cell):

  • A UTC-anchored reading shows a trailing UTC designator (even though its value already ends in Z), so every zone — UTC included — occupies the same zone-designator column that a named zone's abbreviation does.
  • DST is marked with a ☀ sun glyph.

All chrome glyphs are monochrome (egui's GL backend cannot rasterize colour emoji) and are guarded by lens/tests/fonts.rs.

Consequences

  • The frame is legible without a warning symbol; UTC is treated like any other zone for consistency, at the cost of a deliberate Z / UTC duplication.
  • Pure offsets stay reachable (the map, and Etc) but never surface a sign-inverted or duplicate id.
  • These are presentation conventions in lens/src/zone.rs and lens/src/overlay.rs; the engine's PosixNs spine and rendering are unchanged.