feat(openai): prompt cache breakpoints, and bump tinytools for ToolExposure - #146
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Add a provider-neutral marker for explicitly identifying stable prompt prefixes for caching. Providers that do not support explicit breakpoints can ignore it without changing their wire format. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Add optional cache control metadata to text content parts, enabling declared prompt-cache breakpoints while preserving the existing serialization for requests without them. Model the currently supported ephemeral cache lifetime as a typed wire enum. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Route system content through block translation and represent cache breakpoints on OpenAI content parts. This preserves cache directives instead of silently dropping them while validating unsupported breakpoint placement. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Trim excess cache breakpoints to the provider’s maximum of four while retaining the longest cached prefixes. Emit a warning when prompt assembly declares too many breakpoints instead of allowing the request to fail. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Treat cache breakpoints as zero-length, omit them from summaries, and prevent them from satisfying user-query checks so they do not trigger premature compaction or render empty turns. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Add coverage for preserving bare string content without breakpoints, emitting cache controls at valid breakpoints, enforcing provider limits, and keeping markers out of message text. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Update the cache breakpoint tests to reference the translation helper through the local module hierarchy without changing behavior. Auto-committed-on: macbook Co-authored-by: Medulla <medulla@tinyhumans.ai>
Co-authored-by: Medulla <medulla@tinyhumans.ai>
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$0.0215 · 175,360 in / 2,546 out · 24,033 cached (14%) · deepseek/deepseek-v4-flash, openrouter/openai/text-embedding-3-small, z-ai/glm-5.2 · 631 embedded
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security: $0.0124 · 74,762 in / 1,460 out · 24,033 cached (32%) · deepseek/deepseek-v4-flash, z-ai/glm-5.2
tests: $0.0013 · 14,914 in / 109 out · 0 cached (0%) · deepseek/deepseek-v4-flash
description: $0.0007 · 7,496 in / 69 out · 0 cached (0%) · deepseek/deepseek-v4-flash
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📝 WalkthroughWalkthroughAdds ChangesCache breakpoint support
Tinytools vendor pointer
Estimated code review effort: 3 (Moderate) | ~20 minutes Sequence Diagram(s)sequenceDiagram
participant Message
participant translate_user_content
participant OpenAIWire
Message->>translate_user_content: provide message content
translate_user_content->>OpenAIWire: create text and JSON parts
translate_user_content->>OpenAIWire: attach ephemeral cache_control to preceding text
OpenAIWire-->>Message: serialize provider request
Suggested reviewers: Merge Risk: 🟡 Moderate · up to Cache-marked prompts can be rejected when markers span messages or target an incompatible endpoint. These request-generation defects should be fixed before merge. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 16 functions across 7 files. (1 skipped: 1 unsupported.) ✨ Finishing Touches 💡 2⚔️ Resolve merge conflicts 💡
🛠️ Fix failing CI checks 💡
📝 Generate docstrings
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Inline comments:
In `@src/harness/providers/openai/convert.rs`:
- Around line 169-174: Update translate_message and translate_user_content so
CacheBreakpoint triggers multipart content and cache_control serialization only
when the target provider explicitly supports cache control; otherwise preserve
the prior wire shape. Thread the capability through both system and user
translation paths, and add target-specific serialization tests covering
supported and unsupported providers.
- Line 242: Update the request conversion flow around enforce_breakpoint_limit
so breakpoint markers are counted across all assembled ChatMessageWire values,
rather than enforced separately per message. Apply the limit to the complete
request while preserving message assembly, and add a regression test covering
markers split between system and user messages.
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src/harness/message/mod.rssrc/harness/message/types.rssrc/harness/providers/openai/convert.rssrc/harness/providers/openai/test.rssrc/harness/providers/openai/types.rssrc/harness/summarization/render.rssrc/harness/tool/prompt.rsvendor/tinytools
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…tool prompt The CacheBreakpoint content block carries no semantic information relevant to either summarization or user query resolution, so filtering it out in the render step and marking it as false in the resolvable check was redundant. Removing these branches simplifies the code without changing behavior. Auto-committed-on: dragonfly
Update the pinned commit of the tinytools vendored dependency to incorporate upstream changes. Auto-committed-on: dragonfly
1 participant
What
Two things, both prerequisites for the fixed-prefix work in tinyhumansai/openhuman:
1. Prompt cache breakpoints (
edda552…f6d6496). Adds a cache-breakpoint content block to the message model and carries it through the OpenAI translation layer:feat(message): add cache breakpoint content blockfeat(openai): support prompt cache breakpointsfix(openai): preserve cache breakpoints in message contentfix(openai): limit cache breakpoints to provider maximum— providers cap how many breakpoints a request may carry; exceeding it is a request error, so the translation clamps rather than passing them all through.fix(harness): ignore cache breakpoints in message processing— the harness must not treat a breakpoint as content when it walks a transcript.test(openai): cover prompt-cache breakpoint serializationrefactor(openai): use a relative import for message translation2.
chore(vendor): bump tinytools for ToolExposure(485703f). Pins theToolExposureaddition.Dependency
Blocked on tinyhumansai/tinytools#3. The gitlink in
485703fpoints at that PR's branch commit; merge tinytools first, then this needs its gitlink re-pointed at tinytoolsmainbefore merge.Why the breakpoints matter
A turn's fixed prefix — system prompt plus every advertised tool schema — is re-sent on every request. On OpenHuman's orchestrator that was ~19k tokens before the user had said anything. Explicit breakpoints are what let a provider cache that prefix instead of re-reading it each turn, so this is the other half of the work that shrinks the prefix itself.
Testing
cargo test. The serialization test covers the block surviving a round trip and the provider-maximum clamp.Summary by CodeRabbit
New Features
Bug Fixes