teamchong 84b4a3a59a transform: split static/dynamic system text for cache stability ...

Claude Code injects per-turn blocks (<env>, <context>, <git_status>,
<directoryStructure>, <system-reminder>) into the system prompt.
Previously those got rendered into the image alongside the static
slab (CLAUDE.md, agent defs, tool docs), which kills Anthropic's
prompt cache: image bytes drift turn-to-turn → 0% cache hits.

Now we split:
  - static (cacheable)   → image with cache_control: ephemeral
  - dynamic (per-turn)   → plain text block AFTER the image
  - billing line         → also AFTER the image (was BEFORE, also a
                           cache-killer — bug fix as a side effect)

Net effect: stable cache key on the big slab, model still sees cwd /
branch / today's date. Removes the need for users to pass
--exclude-dynamic-system-prompt-sections to claude.

TransformInfo now carries staticChars / dynamicChars / dynamicBlockCount
for downstream telemetry.

Tests: 8 existing pass unchanged + 3 new (env survives as text after
image, cache_control on image only, all-dynamic input is pass-through).

2026-05-18 15:55:21 -04:00

..

render.test.ts

transform: split static/dynamic system text for cache stability

2026-05-18 15:55:21 -04:00