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Both optional capabilities read what earlier questions retrieved and cited from the capability's state, so a host that carries only the message history hands every run an empty record. Compaction then replaced the earlier evidence with receipts and retained nothing, and the loss was invisible: the citations the host already displayed were still there. It now refuses when it finds evidence from an earlier question and no record of what that question cited. `state_carried` reaches the optional capabilities through discovery, so the refusal distinguishes a host that never carries state from a question that simply cited nothing. The documentation taught the pattern that breaks: the compose example is now stateful and the requirement is stated where each capability is introduced. The app's browser storage was doing exactly this, keeping only the fields the UI reads. It now persists the whole namespace map, so the citation policy's violations survive a reload as well as the evidence record.
49 lines
2.1 KiB
Markdown
49 lines
2.1 KiB
Markdown
# Evidence compaction capability
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`EvidenceCompactionCapability` keeps a multi-turn conversation from carrying every
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search result it ever produced. Every question adds its evidence to the history, so
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requests grow turn after turn, which degrades answers and can exceed a provider's
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limits.
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Register it alongside an evidence capability:
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```python
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from pydantic_ai import Agent
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from haiku.rag.capabilities.compaction import create_capability as compaction
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from haiku.rag.capabilities.rag import create_capability as rag
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agent = Agent(
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"openai:gpt-5",
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capabilities=[rag(db_path="my.lancedb"), compaction()],
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)
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```
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It exposes no tools and takes no configuration. Registering it is the only switch:
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leave it out and the transcript reaches the model untouched.
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The host must carry the capability state between runs, alongside the message
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history: the capsule is built from what earlier questions recorded there. Given
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only a message history, every run starts from an empty record, and compaction
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refuses rather than replace evidence it cannot retain. See
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[Compose an agent](index.md#compose-an-agent) for the shape.
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## What it does
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On each request, evidence from earlier questions is replaced by the evidence those
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questions actually cited. Cited text and cited page images are kept in full, grouped by
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the question that cited them, and stay citable by the same chunk ids. Every other
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earlier evidence return becomes a short receipt. The current question is untouched.
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Compaction rewrites the request, never the stored history, so `all_messages()` still
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holds everything the run gathered.
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This reduces what a request carries. It does not bound it: retained evidence still
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grows with the conversation. A host that needs more aggressive pruning can compact its
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own requests further, on the wire only.
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## Resuming a question
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Resuming a question (deferred tool results, an interruption, a suspension) requires the
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host to carry the capability state from the run being resumed, alongside the message
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history. Without it the identity of the question in progress is unknowable, and the run
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fails rather than silently treating it as a new question.
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