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A capsule replaces earlier questions' evidence with what they cited, so the searches that carried a `Collection:` line are gone by the time the model reads it. Cited content survived; which collection it came from did not, and a follow-up question attributed it to whichever the model guessed. Named the same way a search result names it: the capsule decides, and only when it spans more than one.
50 lines
2.2 KiB
Markdown
50 lines
2.2 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. Evidence spanning
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more than one collection carries a `Collection:` line naming the one it came from. Every
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other 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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