# Streaming renderings are append-only (cache-monotone); 2D layouts are keyframe-only

The agent-native live tape is **vertical**: one row per candle, time flowing down,
newest appended last. This is a binding rendering-architecture rule, not a style
choice, because the author is a context window: an append-only rendering is
**KV-cache-monotone** — a long-running agent's entire prior tape remains cached and
each perception update costs O(new bars). A 2D price×time grid (the classic chart
shape) must redraw on every update, invalidating the cache for the whole screen on
every wake; for an agent that watches all day, that is the difference between paying
for a few appended rows and re-paying for the screen hundreds of times.

Therefore: **every Rendering consumed continuously by an agent is append-only**
(delta frames are appended suffixes; state changes arrive as new lines, never as
in-place edits), and **2D layouts are reserved for one-shot keyframes**
(orientation screens, where the redraw happens once by definition) **and for
human-facing formats** (`html` charts of the same Frame). The two-parameter Rendering
model (format × tokenizer) is unchanged; this ADR adds the temporal discipline.

**Row format (a first candidate, not doctrine — graded per ADR-0009): relative
candles with keyframe anchors.** A tape row is candle *shape*,
not levels: direction glyph, body in bps vs prior close, wick extents, volume glyph;
the open is implied by the prior close (a gap prints only when nonzero). Absolute
prices on every row are rejected as tokenizer waste — digit strings fragment under
BPE and every row re-spends the same high-order digits — while small signed integers
tokenize cleanly and remain legible arithmetic the model can reason over (the
**legibility floor**: never compress past interpretable units into opaque symbols;
that converts a reasoning model into a poor tokenizer). Absolute levels live in a
periodic **anchor** (the keyframe re-stamps the level; re-anchor on keyframes and
round-level crosses) and in the levels registry. Exact glyph choices are measured per
target tokenizer, never assumed.

The rejected alternative — leading with 2D ASCII charts and absolute-OHLC rows for
agents — reads better in a screenshot and worse in production: it optimizes the demo,
not the context window. Historical footnote that makes the rule easy to remember: the
original ticker tape was an append-only stream; reading the tape has always meant
reading appended rows.