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, 20 insertions, 2 deletions

diff --git a/Omni/Agent/Subagent/Coder.hs b/Omni/Agent/Subagent/Coder.hs
index 523b035..865a97e 100644
--- a/Omni/Agent/Subagent/Coder.hs
+++ b/Omni/Agent/Subagent/Coder.hs
@@ -17,6 +17,8 @@
 -- : out omni-agent-subagent-coder
 -- : dep aeson
 -- : dep async
+-- : dep directory
+-- : dep mustache
 -- : dep stm
 -- : dep time
 module Omni.Agent.Subagent.Coder
@@ -52,6 +54,7 @@ import qualified Data.Aeson as Aeson
 import qualified Data.Text as Text
 import qualified Data.Time.Clock as Clock
 import qualified Omni.Agent.Engine as Engine
+import qualified Omni.Agent.Prompts as Prompts
 import qualified Omni.Agent.Provider as Provider
 import qualified Omni.Agent.Tools as Tools
 import qualified Omni.Test as Test
@@ -242,7 +245,22 @@ coderTools =
     Tools.searchAndReadTool
   ]
 
--- | System prompt for the Coder subagent
+-- | Load system prompt from template, falling back to hardcoded if unavailable
+loadCoderSystemPrompt :: CoderConfig -> Maybe Text -> IO Text
+loadCoderSystemPrompt cfg maybeInitState = do
+  let ctx =
+        Aeson.object
+          [ "namespace" .= coderNamespace cfg,
+            "task" .= coderTask cfg,
+            "context" .= coderContext cfg,
+            "init_state" .= maybeInitState
+          ]
+  result <- Prompts.renderPrompt "subagents/coder/system" ctx
+  case result of
+    Right prompt -> pure prompt
+    Left _err -> pure (coderSystemPrompt cfg maybeInitState)
+
+-- | Hardcoded fallback system prompt for the Coder subagent
 coderSystemPrompt :: CoderConfig -> Maybe Text -> Text
 coderSystemPrompt cfg maybeInitState =
   Text.unlines
@@ -364,7 +382,7 @@ runWorkVerifyLoop openRouterKey cfg initState verifyAttempt accTokens accCost =
 
   -- Phase 2: Work (run the agent)
   let provider = Provider.defaultOpenRouter openRouterKey (coderModel cfg)
-  let systemPrompt = coderSystemPrompt cfg initState
+  systemPrompt <- loadCoderSystemPrompt cfg initState
   let guardrails =
         Engine.Guardrails
           { Engine.guardrailMaxCostCents = coderMaxCost cfg - accCost,