Optimize deriver prompt prefix caching

src/deriver/prompts.py

@@ -31,6 +31,7 @@ def _custom_instructions_section(custom_instructions: str | None) -> str:
     return c(
         f"""
         CUSTOM INSTRUCTIONS:
+        These instructions apply to the target peer.
         {normalized_custom_instructions}
         """
     )
@@ -54,26 +55,29 @@ def minimal_deriver_prompt(
     custom_instructions_section = _custom_instructions_section(custom_instructions)
     return c(
         f"""
-Analyze messages from {peer_id} to extract **explicit atomic facts** about them.
+Analyze messages to extract **explicit atomic facts** about the target peer.
 
-[EXPLICIT] DEFINITION: Facts about {peer_id} that can be derived directly from their messages.
+[EXPLICIT] DEFINITION: Facts about the target peer that can be derived directly from their messages.
    - Transform statements into one or multiple conclusions
    - Each conclusion must be self-contained with enough context
    - Use absolute dates/times when possible (e.g. "June 26, 2025" not "yesterday")
 
 RULES:
-- Properly attribute observations to the correct subject: if it is about {peer_id}, say so. If {peer_id} is referencing someone or something else, make that clear.
-- Observations should make sense on their own. Each observation will be used in the future to better understand {peer_id}.
-- Extract ALL observations from {peer_id} messages, using others as context.
+- Properly attribute observations to the correct subject: if it is about the target peer, say so. If the target peer is referencing someone or something else, make that clear.
+- Observations should make sense on their own. Each observation will be used in the future to better understand the target peer.
+- Extract ALL observations from the target peer's messages, using others as context.
 - Contextualize each observation sufficiently (e.g. "Ann is nervous about the job interview at the pharmacy" not just "Ann is nervous")
 
 EXAMPLES:
-- EXPLICIT: "I just had my 25th birthday last Saturday" → "{peer_id} is 25 years old", "{peer_id}'s birthday is June 21st"
-- EXPLICIT: "I took my dog for a walk in NYC" → "{peer_id} has a dog", "{peer_id} lives in NYC"
-- EXPLICIT: "{peer_id} attended college" + general knowledge → "{peer_id} completed high school or equivalent"
+- EXPLICIT: "I just had my 25th birthday last Saturday" → "The target peer is 25 years old", "The target peer's birthday is June 21st"
+- EXPLICIT: "I took my dog for a walk in NYC" → "The target peer has a dog", "The target peer lives in NYC"
+- EXPLICIT: "The target peer attended college" + general knowledge → "The target peer completed high school or equivalent"
 
 {custom_instructions_section}
 
+Target peer:
+{peer_id}
+
 Messages to analyze:
 <messages>
 {messages}