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Edit strategies change the message prefix, breaking prompt caching. Use pin_editing_strategies_at_message to keep the prefix stable.

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The Problem

Round 1: [a, b, c]
Round 2: [a(edited), b, c, d]           # cache miss
Round 3: [a(edited), b(edited), c, d, e] # cache miss

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The Solution

Pin where strategies are applied: 
Round 1: [z(edited), a, b, c]           # edit_at_message_id = c
Round 2: [z(edited), a, b, c, d]        # stable prefix ✓
Round 3: [z(edited), a, b, c, d, e]     # stable prefix ✓

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Usage

from acontext import AcontextClient
import os

client = AcontextClient(api_key=os.getenv("ACONTEXT_API_KEY"))

# First call - get the pin ID
result = client.sessions.get_messages(
    session_id="session-uuid",
    edit_strategies=[{"type": "remove_tool_result", "params": {"keep_recent_n_tool_results": 3}}]
)
cache_pin_id = result.edit_at_message_id

# Subsequent calls - pin to maintain cache
result = client.sessions.get_messages(
    session_id="session-uuid",
    pin_editing_strategies_at_message=cache_pin_id,
    edit_strategies=[{"type": "remove_tool_result", "params": {"keep_recent_n_tool_results": 3}}]
)

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When to Reset

When context grows too large, reset by omitting the pin: 
if result.this_time_tokens > 50000:
    result = client.sessions.get_messages(
        session_id="session-uuid",
        edit_strategies=[
            {"type": "remove_tool_result", "params": {"keep_recent_n_tool_results": 3}},
            {"type": "token_limit", "params": {"limit_tokens": 30000}}
        ]
    )
    cache_pin_id = result.edit_at_message_id  # new pin

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Next Steps

Context Editing

Available edit strategies