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>

5 files changed, 77 insertions, 15 deletions

diff --git a/Omni/Agent/Prompts.hs b/Omni/Agent/Prompts.hs
index 231df3c..70414ca 100644
--- a/Omni/Agent/Prompts.hs
+++ b/Omni/Agent/Prompts.hs
@@ -80,7 +80,7 @@ test =
     "Omni.Agent.Prompts"
     [ Test.unit "promptPath constructs correct path" <| do
         let path = promptPath "agents/telegram/system"
-        ("agents/telegram/system.md" `List.isSuffixOf` path) Test.@=? True,
+        ("agents/telegram/system.mustache" `List.isSuffixOf` path) Test.@=? True,
       Test.unit "parsePromptMetadata parses frontmatter" <| do
         let content =
               "---\n\
diff --git a/Omni/Agent/Subagent.hs b/Omni/Agent/Subagent.hs
index f5e04b0..9f3052d 100644
--- a/Omni/Agent/Subagent.hs
+++ b/Omni/Agent/Subagent.hs
@@ -18,6 +18,8 @@
 -- : out omni-agent-subagent
 -- : dep aeson
 -- : dep async
+-- : dep directory
+-- : dep mustache
 -- : dep stm
 -- : dep uuid
 module Omni.Agent.Subagent
@@ -92,6 +94,7 @@ import qualified Data.UUID
 import qualified Data.UUID.V4
 import qualified Omni.Agent.AuditLog as AuditLog
 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.Subagent.Coder as Coder
 import qualified Omni.Agent.Tools as Tools
@@ -611,6 +614,21 @@ toolsForRole Researcher keys =
 toolsForRole Coder _keys = Coder.coderTools
 toolsForRole (CustomRole _) keys = toolsForRole Researcher keys
 
+-- | Load system prompt from template, falling back to hardcoded if unavailable
+loadSystemPromptForRole :: SubagentRole -> Text -> Maybe Text -> IO Text
+loadSystemPromptForRole role task maybeContext = do
+  let ctx =
+        Aeson.object
+          [ "role_description" .= roleDescription role,
+            "task" .= task,
+            "context" .= maybeContext
+          ]
+  result <- Prompts.renderPrompt "subagents/generic/system" ctx
+  case result of
+    Right prompt -> pure prompt
+    Left _err -> pure (systemPromptForRole role task maybeContext)
+
+-- | Hardcoded fallback prompt for subagents
 systemPromptForRole :: SubagentRole -> Text -> Maybe Text -> Text
 systemPromptForRole role task maybeContext =
   Text.unlines
@@ -647,14 +665,14 @@ systemPromptForRole role task maybeContext =
       "}",
       "```"
     ]
-  where
-    roleDescription :: SubagentRole -> Text
-    roleDescription WebCrawler = "web research"
-    roleDescription CodeReviewer = "code review"
-    roleDescription DataExtractor = "data extraction"
-    roleDescription Researcher = "research"
-    roleDescription Coder = "coding"
-    roleDescription (CustomRole name) = name
+
+roleDescription :: SubagentRole -> Text
+roleDescription WebCrawler = "web research"
+roleDescription CodeReviewer = "code review"
+roleDescription DataExtractor = "data extraction"
+roleDescription Researcher = "research"
+roleDescription Coder = "coding"
+roleDescription (CustomRole name) = name
 
 runSubagent :: SubagentApiKeys -> SubagentConfig -> IO SubagentResult
 runSubagent keys config = runSubagentWithCallbacks keys config defaultCallbacks
@@ -778,7 +796,7 @@ runGenericSubagent keys config callbacks = do
   let role = subagentRole config
   let model = fromMaybe (modelForRole role) (subagentModel config)
   let tools = toolsForRole role keys
-  let systemPrompt = systemPromptForRole role (subagentTask config) (subagentContext config)
+  systemPrompt <- loadSystemPromptForRole role (subagentTask config) (subagentContext config)
 
   onSubagentStart callbacks ("Starting " <> tshow role <> " subagent...")
 
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,
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
diff --git a/Omni/Dev/Beryllium/Ava.nix b/Omni/Dev/Beryllium/Ava.nix
index d732249..becbf9e 100644
--- a/Omni/Dev/Beryllium/Ava.nix
+++ b/Omni/Dev/Beryllium/Ava.nix
@@ -83,6 +83,14 @@ in {
     "d /home/ava 0755 ava users -"
     "d /home/ava/omni 0755 ava users -"
     "d /home/ava/skills 0755 ava users -"
+    "d /home/ava/prompts 0755 ava users -"
+    "d /home/ava/prompts/agents 0755 ava users -"
+    "d /home/ava/prompts/agents/telegram 0755 ava users -"
+    "d /home/ava/prompts/shared 0755 ava users -"
+    "d /home/ava/prompts/shared/formatting 0755 ava users -"
+    "d /home/ava/prompts/subagents 0755 ava users -"
+    "d /home/ava/prompts/subagents/generic 0755 ava users -"
+    "d /home/ava/prompts/subagents/coder 0755 ava users -"
     "d /home/ava/outreach 0755 ava users -"
     "d /home/ava/outreach/pending 0755 ava users -"
     "d /home/ava/outreach/approved 0755 ava users -"