The per-turn `<system-context>` block opened with `Now: YYYY-MM-DD HH:MM` (2c9fb74,
2026-08-20) so that absolute scheduling had a clock. The block is glued onto the last
user message — the task prompt in a tool loop — and a provider's prompt cache is
reusable only up to the first byte that differs, so every minute crossing rewrote
message one and re-processed the whole conversation. 9d6a716 worked around it with a
trailing-message shape, an Anthropic-only relocation of that message, and a
`live_clock` switch that headless runs set off. This commit removes the cause instead
and deletes the workarounds; the shape is the same on every provider again.
- The block carries no clock, on any provider. What is left (folders, skill menu,
mode notices, memory-off notice, disable countermand) changes only when the user
changes something, so the outbound history is byte-identical turn to turn.
- `current_time` tool (coworker/clock.py), registered for every persona: local time
with offset and zone, the same instant in UTC, weekday. The environment block's
"Today's date" now says it is a session-start snapshot and points at the tool.
- `sleep_for(seconds)` is back beside `sleep_until` (a relative wait needs no clock
arithmetic; the four lead personas' manifests still told the model to call
sleep_for, which 2c9fb74 had removed). `sleep_until`'s description points at
current_time for the date/timezone. Timer wake messages carry their fire time.
- Deleted: `live_clock` config + COWORKER_LIVE_CLOCK, the trailing-message shape in
`_outbound_messages`, `_relocate_ephemeral_note` in the Anthropic provider. The
cache-diagnostics instrument (off by default) stays.
Validation runs (one long tool-heavy task, one attempt each on Fable 5.1 and Kimi K3,
compared with the 9d6a716 runs of the same task) are recorded on OPE-192.
Tests: tests/test_clock_tool.py (new), tests/test_context_block_placement.py and
tests/test_cache_breakpoint_placement.py rewritten for the single shape,
tests/test_live_clock.py removed; self-wake, attachments, message-source and
multiroot tests updated. Full suite unchanged against the Windows baseline.
