Report what a reply spent reading its prompt, and pin the clock right

`UsageDelta` gains `prefillMs`, llama-server's own `timings.prompt_ms`, so the
footer under a finished reply is "read 9.5s · 50.3 tok/s · 3:00 PM". Prefill is
the half of a turn that was invisible and is often the larger: measured on the
0.6B here, 1m 4s for the first turn after a model loads against 22ms for the
next, whose prompt the server still had cached.

The clock moves to the end of the line. Everything in front of it is a
provider's own measurement, so a session on another provider has fewer of them
or none, and a reader who has learned where the time is should not have to find
it again because the model changed. The costs grow leftwards into the space
instead, and a test asserts every shape of the line ends with the same thing.

Verified on the emulator against a real llama session: three replies reading
"read 1m 4s · 193 tok/s · 3:54 PM", "read 25ms · 308 tok/s · 3:54 PM" and
"read 22ms · 194 tok/s · 3:54 PM", with the clock in one column.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

PLAN.md

@@ -169,13 +169,17 @@ seq N", so there is no separate history path to drift from the live one.
   waiting for itself and will speak again with nobody having typed anything.
   Reporting it as idle sent a "finished" notification at the one moment that
   was untrue.
-- `UsageDelta { tokens, context, tokensPerSecond }` — what a turn cost, how
-  much the model was holding when it ended, and how fast it was generated.
-  `tokensPerSecond` (2026-09-19) is the provider's own measurement or nothing:
-  llama.cpp reports `timings.predicted_per_second`, and the coding CLIs report
-  no such figure, so dividing what this server watched a reply arrive over
-  would count the network, the tool calls and the reader's own permission
-  answers as generation. The phone draws it under the reply it measured. `context` is prompt plus both cache figures,
+- `UsageDelta { tokens, context, tokensPerSecond, prefillMs }` — what a turn
+  cost, how much the model was holding when it ended, how fast it was
+  generated, and how long the provider spent reading the prompt first. The last
+  two (2026-09-19) are the provider's own measurements or nothing: llama.cpp
+  reports `timings.predicted_per_second` and `timings.prompt_ms`, and the
+  coding CLIs report neither, so dividing what this server watched a reply
+  arrive over would count the network, the tool calls and the reader's own
+  permission answers as generation. The phone draws both under the reply they
+  measured. `prefillMs` is small on a turn whose prompt the server still had
+  cached -- 22ms against 64s for the first turn after a model loads, measured
+  on the 0.6B -- which is a fact about the turn rather than a missing figure. `context` is prompt plus both cache figures,
   taken from the **last assistant message** rather than the turn's `result`:
   measured 2026-08-30 against CLI 2.1.237, the result adds a turn's messages
   up, so its cache read of 40,211 was the same conversation counted twice.
@@ -1275,14 +1279,17 @@ dev-updater (Kotlin 2.4.x, CMP 1.11.x, JDK 21).
      the model stopped to think in the middle of it. A block cut by a page
      boundary is welded like a reply is (`healSplitThinking`), since the half
      with no ending would otherwise spin for the rest of the conversation.
-   - **A finished reply carries a line under it saying when it was sent and,
-     where the provider measured one, how fast it was generated** (2026-09-19)
-     — "3:00 PM · 149 tok/s", small and set back, right-aligned because it
-     closes the message rather than opening one. The time is the transcript's
-     own timestamp, so every device draws the same one; the rate is the
-     provider's own figure or nothing at all. It is a list unit of its own
-     (`ReplyFoot`), because a settled reply *is* its blocks and there is no
-     row left to hang it on.
+   - **A finished reply carries a line under it saying what it cost to produce
+     and when it was sent** (2026-09-19) — "read 9.5s · 50.3 tok/s · 3:00 PM",
+     small and set back, right-aligned because it closes the message rather
+     than opening one. **The clock is last**, so it sits against the right edge
+     whatever else is on the line: the measurements in front of it belong to
+     the provider, and a reader who has learned where the time is should not
+     have to find it again because the session is on a different one. The time
+     is the transcript's own timestamp, so every device draws the same one; the
+     costs are the provider's own figures or nothing at all. It is a list unit
+     of its own (`ReplyFoot`), because a settled reply *is* its blocks and
+     there is no row left to hang it on.
    - **Anything that is a note *about* the conversation rather than a turn in
      it is closed by default** — a tool call, a peer message, a memory note,
      a thinking block.