A time in no particular zone, and a preview missing what it previews

The first audit pass: everything from 0.8.1 to 0.9.8 read as a whole rather
than one feature at a time, starting with what a model is actually told.

Four of these had shipped as correct. The date line carried a timezone
variable that resolves to nothing until somebody chooses one -- so every
default account was told times were "in  unless they say otherwise", while
two comments asserted the line disappeared instead. The prompt preview
built its variables without a chat, which is what eleven fragments are
gated on, so the whole agent surface was absent from it whatever was
ticked. Plan mode was instructed to keep its plan current with a tool that
mode withdraws. And knowledge_get returned a document whole where every
sibling reader caps and says so, its description promising exactly that.

The subagent guidance was wrong in both directions at once: it denied a
documented parameter and named seven of twenty-three allowed commands.
Both halves are pinned by tests against the real list and the real schema
now, because prose and a constant drift the moment one is edited alone.

docs/notes/audit-0.9.md carries the findings that are not fixed here, with
why -- the ones whose fix would change what a feature does are the user's
call, not this pass's.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/lembas/services/harness.py

@@ -188,10 +188,23 @@ def context_variables(
         "today": stamp.strftime("%A %-d %B %Y"),
         "now": stamp.strftime("%A %-d %B %Y, %H:%M (UTC%z)"),
         # Named so a model working out a schedule can say which zone it meant,
-        # and so `core.today` can carry it without a second fragment. Empty when
-        # nobody has chosen one, which drops the line rather than printing the
-        # server's zone as though it were a decision.
-        "timezone": clock.name_for(user),
+        # and so `core.today` can carry it without a second fragment.
+        #
+        # The fallback is load-bearing and used to be absent. `name_for` returns
+        # "" for anybody who has never chosen a zone -- the default state of
+        # every account -- and the comment here claimed that dropped the line
+        # rather than announcing the server's zone as a decision. It did not:
+        # `substitute` drops a line only when it is *blank* after expansion, and
+        # this variable sits inside a sentence, so every such request shipped
+        # "- Times the person gives you are in  unless they say otherwise."
+        #
+        # Naming the server's zone was never the thing being avoided anyway.
+        # `stamp` is `clock.now_for(user)`, which already falls back to it, so
+        # `{{today}}` and `{{now}}` are *already* in that zone and `{{now}}`
+        # already prints its offset. Withholding the label from a value the
+        # model has been given is not restraint, it is a hole. This is the
+        # fallback `schedule/compile.py` has always had, for the same reason.
+        "timezone": clock.name_for(user) or str(clock.server_zone()),
         "instance_name": branding.for_db(db).name,
         "user_name": (user.name or "") if user is not None else "",
         "model_name": "",
@@ -241,6 +254,7 @@ def context_variables(
         "agent_instructions": "",
         "agent_instructions_file": "",
         "plan": "",
+        "plan_editable": "",
         # Empty everywhere but a scheduled task's own chat, which is what makes
         # it the gate on `core.unattended` as well as the content of
         # `context.schedule`. Two fragments, one variable, and no way for the
@@ -346,6 +360,17 @@ def _agent_values(db: DBSession, chat, user) -> dict[str, str]:
         # `agent_session.resolve`. A plan the model cannot see is a plan it
         # cannot keep current, which is the whole of why this is here.
         "plan": plans_service.render_block(context.plan),
+        # Whether `plan_update` is actually in this request, which is not the
+        # same question as whether there is a plan. `agent/tools.py` drops it in
+        # Plan mode -- that mode ends with `plan_submit` instead -- so gating its
+        # guidance on `plan` alone told a model in Plan mode to "keep it current
+        # with plan_update as you go" about a tool that was not there, directly
+        # under `core.tool_list` saying anything unnamed does not exist. The
+        # fragment's own hint claimed the two coincided. They do not, and this
+        # is the variable that makes them.
+        "plan_editable": (
+            plans_service.render_block(context.plan) if context.mode != policy.MODE_PLAN else ""
+        ),
         **_project_instructions(db, chat, context, settings_store),
     }