Omni/Agent: wire prompt templating system to agents

- Telegram.hs: add loadTelegramSystemPrompt with fallback
- Subagent.hs: add loadSystemPromptForRole with fallback
- Coder.hs: add loadCoderSystemPrompt with fallback
- Ava.nix: add tmpfiles rules for /home/ava/prompts/
- Prompts.hs: fix test to expect .mustache extension

Templates loaded at runtime from $AVA_DATA_ROOT/prompts/.
Falls back to hardcoded prompts if templates not found.

Amp-Thread-ID: https://ampcode.com/threads/T-019b3878-73be-77ec-97cc-d092a28d211e
Co-authored-by: Amp <amp@ampcode.com>

1 files changed, 21 insertions, 3 deletions

diff --git a/Omni/Agent/Telegram.hs b/Omni/Agent/Telegram.hs
index 0ebf4ca..7b2beaa 100644
--- a/Omni/Agent/Telegram.hs
+++ b/Omni/Agent/Telegram.hs
@@ -13,7 +13,9 @@
 --
 -- : out omni-agent-telegram
 -- : dep aeson
+-- : dep directory
 -- : dep http-conduit
+-- : dep mustache
 -- : dep stm
 -- : dep HaskellNet
 -- : dep HaskellNet-SSL
@@ -85,6 +87,7 @@ import qualified Omni.Agent.AuditLog as AuditLog
 import qualified Omni.Agent.Engine as Engine
 import qualified Omni.Agent.Memory as Memory
 import qualified Omni.Agent.Paths as Paths
+import qualified Omni.Agent.Prompts as Prompts
 import qualified Omni.Agent.Provider as Provider
 import qualified Omni.Agent.Skills as Skills
 import qualified Omni.Agent.Subagent as Subagent
@@ -154,8 +157,20 @@ test =
 benChatId :: Int
 benChatId = 33193730
 
+-- | Load system prompt from template, falling back to hardcoded if unavailable
+loadTelegramSystemPrompt :: IO Text
+loadTelegramSystemPrompt = do
+  result <- Prompts.renderPrompt "agents/telegram/system" (Aeson.object [])
+  case result of
+    Right prompt -> pure prompt
+    Left _err -> pure telegramSystemPromptFallback
+
+-- | Hardcoded fallback prompt (used if template not found)
 telegramSystemPrompt :: Text
-telegramSystemPrompt =
+telegramSystemPrompt = telegramSystemPromptFallback
+
+telegramSystemPromptFallback :: Text
+telegramSystemPromptFallback =
   Text.unlines
     [ "don't worry about formalities. respond conversationally, in short messages, not long essays. ask follow up questions before answering if you need to.",
       "",
@@ -1100,8 +1115,11 @@ processEngagedMessage tgConfig provider engineCfg msg uid userName chatId userMe
                 "prioritize: urgent items first, then emails needing response, then suggest unsubscribing from marketing."
               ]
           else ""
-      systemPrompt =
-        telegramSystemPrompt
+
+  basePrompt <- loadTelegramSystemPrompt
+
+  let systemPrompt =
+        basePrompt
           <> "\n\n## Current Date and Time\n"
           <> timeStr
           <> chatContext