Goal: lift prompt-cache hit rate from the ~75% baseline toward 95%+
on DeepSeek/MiMo-style 64-token chunked prefix caches. Both providers
match a stable byte-identical prefix from message[0]; once a single
byte changes everything after it misses, so the trick is to push every
session-stable bit to the front and concentrate per-call churn in a
short suffix.
Three coordinated changes:
1. Split storyState rendering into spine + dynamic.
renderStoryStateSpine: logline / genreTags / protagonist / castNotes
— Architect-set fields that StoryStatePatch literally cannot touch
(the type only declares the 4 volatile ones; coerce and apply both
cherry-pick), so spine bytes are guaranteed stable for the entire
session. Goes in the STABLE PREFIX.
renderStoryStateDynamic: synopsis / openThreads / relationships /
nextHook — the Writer rewrites these every scene via storyStatePatch.
Goes in the DYNAMIC SUFFIX.
renderStoryState kept as a convenience wrapper that joins both, for
anything that still wants the merged bible.
2. Rewrite buildWriterUserMessage with a stable/dynamic split.
STABLE PREFIX (byte-identical or pure append across consecutive calls):
- 世界观 / 画风 (session-immutable scalars)
- story bible spine
- 已登记角色 [sentinel: "（以下每行一个已登记角色，开场前为空。）"] + entries
- 已使用的 sceneKey [sentinel] + entries
- 场景历史，已完结 [sentinel] + archivedHistory entries
↑ archivedHistory = history.slice(0, -1), NOT the full history
— the live entry (history[-1]) keeps mutating mid-scene as the
player walks new beats and speculative prefetches snapshot it
at different moments, so it MUST stay out of the stable prefix
or the byte-monotonic invariant breaks.
DYNAMIC SUFFIX:
- storyState dynamic patch
- last-beat snippet (the exact emotional cliffhanger to continue from)
- lastExit hint
- format reminder tail
The previous structure put the full storyState (including patched
fields) at the very top of the user message, so the very first byte
of the user message changed every scene — user-side cache hit was
effectively 0% across the board.
3. Sentinel pattern for variable-length sections.
Every list (characters / sceneKeys / archivedHistory) now emits a
constant placeholder line after its header REGARDLESS of whether
it has entries. With the old "if empty print '（暂无）' else print
entries" pattern, adding the first item silently rewrites those
placeholder bytes — the byte at offset N moves from a Chinese
parenthesis to a dash, prefix cache torched. The sentinel line is
the same bytes whether the list has 0 or N items; new items are
pure appends after it.
4. Rewrite buildCinematographerUserMessage.
New CINE_STABLE_HINT constant (~80 tokens of fixed guidance) glued
right after the session-stable styleGuide line, so the stable prefix
is long enough to cross at least one full 64-token chunk boundary
beyond the system prompt. The per-scene inputs (sceneSummary,
entryBeatActive, entryBeatSpeaker policy, prior-sceneKey continuity
hint) all moved into the dynamic suffix below.
Verified (see [cache] / [debug-writer] logs from staging): hash of
500-byte slices of the user message is byte-identical across two
same-historyLen Writer calls through the entire stable prefix; only
the dynamic suffix slice differs. The remaining cache-hit gap under
MiMo is a server-side quirk (hit plateaus near 3072 tokens, occasionally
jumps to 4096); on DeepSeek the same prefix should hit fully.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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