refactor(schedule): simplify request zone authority

.agents/notes/implemented/feature/2026-08-05-durable-web-schedule.md

@@ -33,15 +33,15 @@ An Agent-scoped FIFO serializes each accepted management transaction and the liv
 
 Every successful management preflight also asks the live owner to recompute. This closes the recovery path where create appended successfully but its post-append barrier rejected: a later list can confirm the coordinator's retained batch, return the active record, and arm its timer without a Schedule-specific retry loop.
 
-### Session and request time-zone authority
+### Session and request time-zone ownership
 
 The official Web create path requires the browser's IANA zone, validates and canonicalizes it at the Host boundary, and stores it once as immutable `SessionHeader.timeZone`. Resume preserves that value, fork copies it, and another create for the same id and cwd conflicts when its canonical zone differs. Session core keeps the field optional so pre-zone Sessions remain readable but explicitly `unavailable`; a legacy header is never backfilled from a later browser request. JSONL preserves the optional header, while SQLite schema v14 adds nullable `time_zone` and upgrades an owned v13 database atomically without guessing values for existing rows.
 
 Every Web prompt samples its own `clientTimeZone`, which the Host validates before Agent entry and binds to that immutable `user-rpc` message source. This is request provenance, not a mutable property of the connection or Session, so concurrent tabs cannot overwrite one another and queue, steering, edit, retry, and persisted history retain the originating zone.
 
-Time-context opens a request-authority envelope at system-prompt assembly. Its model-visible reading uses the Session zone for the current date, local time, and offset, while its machine source names the proposed turn and step plus Session `resolved`/`unavailable` and client `resolved`/`mixed`/`missing` state. Steering admitted during asynchronous assembly is followed synchronously by a same-step superseding authority; the model and Schedule tool both consume the last authority for that turn and step. AgentLoop drains only the closed envelope that begins and ends with those authority messages. If the proposed step exits before `step/start`, it settles appendable authority inside the failed turn or removes authority that cannot be appended, while preserving the existing steering policy, so an old turn/step authority cannot leak into a later request.
+Time-context delegates through `agent/pre-step`, derives the final entered request's zones from the immutable Session header and message-bound browser sources, and appends one model-visible reading to an entered step. Its source remains the simple plugin marker; it does not copy those facts into another durable authority. Steering inserted after AgentLoop claims the current batch keeps ordinary next-step ownership and receives fresh context when that step enters. Rejection, cancellation, or failure before `step/start` records no reading, and this feature adds no inbox or AgentLoop lifecycle state.
 
-An implicit local `at` is accepted only when the final authority has one resolved client zone equal to the resolved Session zone. A headerless Session, missing or mixed client provenance, or a client/Session mismatch returns `timezone_confirmation_required` with the known zones. An explicit `time_zone` bypasses that ambiguity check but still passes the same IANA validation.
+Schedule requires a current-step time-context marker, then derives request zones directly from the open turn's original `user-rpc` sources. An implicit local `at` is accepted only when that derivation has one client zone equal to the Session zone. A headerless Session, missing or mixed client provenance, or a client/Session mismatch returns `timezone_confirmation_required` with the known zones. An explicit `time_zone` bypasses that ambiguity check but still passes the same IANA validation.
 
 ### Absolute-time normalization
 
@@ -107,7 +107,7 @@ The design does not recognize or migrate any unmerged Schedule implementation or
 
 Package tests pin strict decoding, transitions, fork suffixes, id reuse, offset and local-calendar profiles, IANA validation, gap rejection, overlap-first selection, mismatch confirmation, time bounds, bounded waits, wall-clock movement, overdue admission, fixed framing, enqueue and append failures, barrier recovery, registration rollback, and quiescent disposal at 100% per-file coverage. Persistence tests cover new, fork, and resumed initialization failures against the actual durable cursor, optional header round-trips, a real SQLite v13-to-v14 migration, and a production JSONL restart. The assembled Loader/Web restart lane proves pending recovery, fork isolation, one durable dispatch, cold-history rendering without Agent activation, and no redelivery after another restart. Host/client tests cover zone identity across live, stored, and concurrent-create paths; per-operation prompt provenance; commit gating; reversed watermarks; semantic header identity; per-event prefix matching; same-seq upgrades; every window merge exit; and reconnect generations.
 
-Time-context and AgentLoop lifecycle tests cover queued, edited, discarded, cancelled, and retried input; mixed tabs; delayed assembly with late steering; pre-step hook, assembly, checkpoint, append, and disposal failures; same-step last-authority selection; and non-leakage into the next turn. The opt-in Loader composition boots the source and built packages. Keyless real-browser scenarios execute `schedule_create` through the complete tool pipeline for the existing short `after` case and one absolute-time case, observe the identity-matched persisted prefix, and render the durable reminder card from attached history. The deliberately absent model adapter closes the turn with an error after dispatch, proving that model failure does not remove the receipt.
+Time-context tests cover final pre-step messages, current-turn unique/mixed/missing zone derivation, post-claim steering entering the next step, cancellation, empty suppression, retry, simple source validation, and in-flight disposal. Schedule tests independently derive the same request zones from durable `user-rpc` sources and fail closed without a current-step marker. The opt-in Loader composition boots the source and built packages. Keyless real-browser scenarios execute `schedule_create` through the complete tool pipeline for the existing short `after` case and one absolute-time case, observe the identity-matched persisted prefix, and render the durable reminder card from attached history. The deliberately absent model adapter closes the turn with an error after dispatch, proving that model failure does not remove the receipt.
 
 ## Consequences