# The P0 benchmark fixture

`transcript.jsonl` is a synthetic transcript in the app's event model (the JSON lines
`GET /sessions/{id}/transcript` returns; see `event-model` and
`server/src/session/driver.rs`) -- never a real one. The `bench` build opens it without a
server so renderer measurements use deterministic data.

Generated by `./generate.py` (Python stdlib only, seeded -- `SEED = 20260905` -- so re-running it
reproduces the same file byte for byte). It writes into `assets/`; only those generated assets are
embedded in the benchmark APK.

- `transcript.jsonl` -- 3,603 events. The first 3,202 (`BACKLOG_COUNT`) are the scrolled-back
  history the benchmark opens with: user turns, tool calls with kilobyte-scale input/output,
  assistant replies built from headings, bold/italic/inline code, a link, fenced code blocks that
  rotate through rust/kotlin/python/sh/json/toml, a markdown table, two embedded images, and
  periodic `usageDelta`/`compacted` events. The remaining 400 (`STREAM_COUNT`) are not part of the
  opening window -- both bench harnesses replay them at a fixed rate (20/s) through the same live
  fold path a real SSE reply arrives on, which is P0's "streaming phase."

  **The streamed reply has a blank line every few deltas** (2026-09-09), so the markdown block a
  delta lands in stays the size a real reply's blocks are -- 53 blocks, longest 502 characters,
  against a measured p50 of 147 and a largest-ever 1,580 over 7,706 blocks of real assistant
  messages. It used to be one run-on 14,888-character block, and since a row re-shapes the block a
  delta lands in, every delta re-shaped all of it: quadratic in the reply's length, and 9.5ms of
  frame time on a phone spent on a shape that does not occur. docs/RUST.md's "Incremental text"
  has the measurements.

  **The run-on message is kept**, as the first two events of the backlog: 14,824 characters in a
  single block, just under `text_cap`'s 16 KiB `MESSAGE_BYTES` so it draws in full rather than
  behind a "Show all". It is deliberately *not* streamed -- the repeated-reshape pathology needs a
  growing block, and that lives in the UI profiling rig where it can be iterated on
  in a second rather than in a two-minute phone run. It is emitted with the random state saved and
  restored around it, so adding it left every other backlog event byte-identical; that is what
  keeps `phone_screen.rs`'s recorded gestures landing on the content they were recorded against.
- `bench1.png`, `bench2.png` -- tiny (8x8) flat-colour PNGs, base64-free on disk but served the
  same way a real attachment is (`GET /sessions/{id}/files/{name}`), referenced by the two
  `"type":"image"` events in the transcript.

`BACKLOG_COUNT` lives here, in `generate.py`, and in `app/src/ui/fixture.rs`; change all three
together. The split is by line index.

Regenerate after changing the shape (a new event type, a different backlog/stream split) with
`./generate.py`, and commit the result -- it is checked in rather than generated at build time so
the benchmark embeds identical bytes without needing this script at build time.