| name | roo-fix-volatile-msg |
| description | Ladder-aware Roo Code Anthropic caching — verify the rolling read/write ladder on the wire, then close the real gaps (Vertex 4-block budget, MiniMax path). |
| target_harness | Roo Code |
| target_repo | RooCodeInc/Roo-Code |
| target_files | ["src/api/transform/caching/anthropic.ts","src/api/providers/anthropic.ts","src/api/providers/anthropic-vertex.ts","src/api/providers/minimax.ts"] |
| target_commit | v3.54.0 (ladder verified live 2026-08-28; transform moved to src/api/transform/caching/) |
| estimated_savings | avoids a harmful "fix" + protects Vertex 4-block budget |
Roo Code: the "volatile message" is a rolling ladder — verify, don't rip out
REANALYZED 2026-08-28. The previous version of this skill
replaced Roo's last-two-user-messages marking with a single "last
stable message" breakpoint. Direct source recon shows Roo (a Cline
fork) carries the same documented rolling read/write ladder as
Cline — the inline comment explains it verbatim. Applying the old
diff would remove a working cache write point. Verify the ladder
instead; the real Roo-specific wins are below.
Target
src/api/transform/caching/anthropic.ts in RooCodeInc/Roo-Code
(moved there by v3.54.0 — the ladder function addCacheBreakpoints
lives in that file now; src/api/providers/anthropic.ts calls it).
Permalink: https://github.com/RooCodeInc/Roo-Code/blob/v3.54.0/src/api/transform/caching/anthropic.ts
What Roo actually does
Same shape as Cline (see
cline-fix-volatile-msg for the
full ladder explanation — Roo's inline comment documents it
verbatim): current user turn = write point, previous user turn = read
point, system prompt has its own breakpoint.
Step 1 — verify the ladder on the wire (before any change)
Same 3-turn capture as the Cline skill. Ladder holds → leave the
breakpoints alone. Thrash → real bug, apply the Cline skill's
diagnosis. Do not skip this step on the strength of the source code
alone — the ladder only proves itself on the wire.
Step 2 — Vertex: respect the 4-block budget explicitly
Roo's anthropic-vertex.ts documents Vertex-specific limits: max 4
cache_control blocks, text-only, user/assistant restrictions — and
implements an explicit strategy (system + last text block of each of
the last two user messages). If you patch message-level caching on
direct Anthropic, make sure the Vertex path still fits its own budget:
- System prompt: 1 block
- Last text block of second-to-last user message: 1
- Last text block of last user message: 1
- → 3 used, 1 spare. Any added breakpoint must not be a 4th on Vertex
unless it replaces a message breakpoint.
Step 3 — OpenAI-native lanes: the missing prompt_cache_key
Roo scans show zero prompt_cache_key usage across the codebase
(665 TS files checked, 2026-08-28). Its OpenAI-native handler relies
on automatic prefix matching only. That works for single-session use
but leaves multi-worker pod routing to chance — the same gap Cline
has. See cline-openai-cache-key
for the hash-derivation pattern; the same fix applies to
src/api/providers/openai-native.ts (derive the key from system
prompt + model slug, NOT a per-session UUID).
Step 4 — MiniMax / anthropic-compat providers inherit the ladder
Roo's minimax.ts handler (and any Anthropic-compatible provider
added later) re-implements addCacheControl with the same
last-two-user-messages shape. Any future provider handler copied from
it inherits the ladder — apply the same verify-don't-rip rule, and
check the compat endpoint actually honors cache_control (gotcha 17:
a 200 response proves nothing).
Verify (whole skill)
3-turn capture on the direct Anthropic path unchanged in shape;
Vertex capture shows ≤4 blocks per request; OpenAI path shows stable
prompt_cache_key across turns and non-zero cached_tokens by turn 2.
Background
