fix: session timestamps and log filenames use UTC (toISOString()) instead of local time

[v4ever1luv]

Describe the bug

Session titles and log filenames use
ew Date().toISOString(), which always returns UTC time. On systems with non-UTC timezones (e.g. UTC+07:00), timestamps are displayed 7 hours off from local time, causing confusion when users try to identify sessions or correlate logs with local events.

Steps to reproduce

1. Open opencode TUI (v1.15.13) on Windows with timezone UTC+07:00 (SE Asia Standard Time)
2. Start a new session — title shows \New session - 2026-06-01T17:00:00.000Z\ instead of local \2026-06-02T00:00:00\
3. Enable /timestamps\ — message timestamps also display in UTC
4. Check log files in ~/.local/share/opencode/logs/\ — filenames use UTC timestamps

Expected behavior

Session titles, message timestamps, and log filenames should reflect the system's local timezone, not UTC.

Actual behavior

All timestamps are hardcoded to UTC via
ew Date().toISOString().

Root cause locations

Two source files use \ oISOString():

1. *\packages/opencode/src/session/session.ts* — session title generation
2. *\packages/opencode/src/util/log.ts* — log filenames and log entry timestamps

\ oISOString()\ is defined by ECMAScript to always return UTC (ending in \Z), ignoring the system \TZ\ environment variable.

Proposed fix

Replace \ oISOString()\ with a local-time-aware formatter:

\\ ypescript
function toISOLocal(d: Date): string {
const z = (n: number) => String(n).padStart(2, '0');
const off = d.getTimezoneOffset();
const sign = off > 0 ? '-' : '+';
const absOff = Math.abs(off);
return \--\T::\:\;
}
\\

Or alternatively, use \Intl.DateTimeFormat\ or a library like \date-fns/\dayjs\ for more robust formatting.

Related issues

• Session timestamps display in UTC instead of local time #9025 — UTC timestamps reported
• fix(opencode): log timestamps use local datetime instead of UTC ISO string #21330 — log timestamps fix (auto-closed due to template)
• [FEATURE]: Default session title should use local time instead of UTC (Z) #22781 — session title local time request

Environment

• OpenCode version: v1.15.13
• Platform: Windows
• Timezone: UTC+07:00 (SE Asia Standard Time)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Default session title should use local time instead of UTC (Z) #22781: Open feature request for default session title to use local time instead of UTC
• Session timestamps display in UTC instead of local time #9025: Previously closed bug report about session timestamps displaying in UTC instead of local time
• Session permanently unresponsive when message timestamps are ~7h ahead of real wall clock time Repository: anomalyco/opencode #26159: Open issue about session timestamps being ~7h ahead of real wall clock time

If your issue is distinct from these, please clarify what is different. Otherwise, consider adding your input to one of the existing issues.

[v4ever1luv]

This issue is distinct from #22781 and #9025 in that it covers 3 areas, not just session titles:

1. Session title (session.ts) - same as [FEATURE]: Default session title should use local time instead of UTC (Z) #22781
2. Log filenames (util/log.ts) - same as fix(opencode): log timestamps use local datetime instead of UTC ISO string #21330, still unfixed
3. Message timestamps in TUI (/timestamps command) - currently bugged per /timestamps command has no visible effect and /exit missing from autocomplete #26625

I'm working on a PR that addresses all 3 with a unified local-time formatter. Will link it here shortly.

[v4ever1luv]

Created PR #30350 that fixes this issue by replacing toISOString() with local-time formatting in session.ts, log.ts, and trace.ts.