Summary

Add a new ui.output.time_format config option to allow users to customize timestamp display format in message headers. Also fixes a locale encoding issue on Chinese Windows where os.date('%b') returns GBK-encoded characters (e.g. 5月 → displayed as 5<d4><c2>).

Changes

lua/opencode/config.lua

• Added time_format = nil default under ui.output

lua/opencode/types.lua

• Added ---@field time_format string|nil to OpencodeUIOutputConfig

lua/opencode/util.lua

• If time_format is set, uses it directly via os.date(time_format, timestamp)
• When nil (default), wraps locale-sensitive os.date('%X', ...) and os.date('%b', ...) calls in os.setlocale('C', 'time')/restore pairs to prevent non-UTF-8 output

tests/unit/util_spec.lua

• Updated test helpers to use C locale for comparison, matching the new behavior

Usage

require('opencode').setup({
  ui = {
    output = {
      time_format = '%m/%d %H:%M',  -- e.g. "05/21 19:13"
    },
  },
})

When unset (nil), behavior matches the original format but with the encoding bug fixed.