jr: add 'prompt' command to inspect agent system prompt

jr prompt <task-id> constructs and prints the full system prompt
that would be sent to the agent, including:
- Agent configuration (model, cost budget)
- Base instructions
- AGENTS.md content
- Relevant facts from knowledge base
- Retry/progress context if applicable

Useful for debugging agent behavior and token usage.

2 files changed, 71 insertions, 1 deletions

diff --git a/Omni/Agent/Worker.hs b/Omni/Agent/Worker.hs
index 45caf9b..110c929 100644
--- a/Omni/Agent/Worker.hs
+++ b/Omni/Agent/Worker.hs
@@ -1,7 +1,13 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 
-module Omni.Agent.Worker where
+module Omni.Agent.Worker
+  ( start,
+    buildFullPrompt,
+    selectModel,
+    selectCostByComplexity,
+  )
+where
 
 import Alpha
 import qualified Data.Aeson as Aeson
@@ -575,3 +581,50 @@ formatFact f =
            then ""
            else " [" <> Text.intercalate ", " (TaskCore.factRelatedFiles f) <> "]"
        )
+
+-- | Build the full system prompt for a task without starting the agent.
+-- This is useful for debugging/inspecting what the agent will be told.
+buildFullPrompt :: TaskCore.Task -> IO Text
+buildFullPrompt task = do
+  repo <- Directory.getCurrentDirectory
+  let ns = fromMaybe "." (TaskCore.taskNamespace task)
+  let basePrompt = buildBasePrompt task ns repo
+
+  maybeRetry <- TaskCore.getRetryContext (TaskCore.taskId task)
+  progressContent <- TaskCore.getProgressSummary (TaskCore.taskId task)
+
+  let progressPrompt = buildProgressPrompt progressContent
+  let retryPrompt = buildRetryPrompt maybeRetry
+  let prompt = basePrompt <> progressPrompt <> retryPrompt
+
+  agentsMd <-
+    fmap (fromMaybe "") <| do
+      exists <- Directory.doesFileExist (repo </> "AGENTS.md")
+      if exists
+        then Just </ readFile (repo </> "AGENTS.md")
+        else pure Nothing
+
+  relevantFacts <- getRelevantFacts task
+  let factsSection = formatFacts relevantFacts
+
+  let systemPrompt =
+        prompt
+          <> "\n\nREPOSITORY GUIDELINES (AGENTS.md):\n"
+          <> agentsMd
+          <> factsSection
+
+  let model = selectModel task
+  let costBudget = selectCostByComplexity (TaskCore.taskComplexity task)
+
+  pure
+    <| Text.unlines
+      [ "=== AGENT CONFIGURATION ===",
+        "Model: " <> model,
+        "Cost budget: " <> tshow costBudget <> " cents",
+        "",
+        "=== SYSTEM PROMPT ===",
+        systemPrompt,
+        "",
+        "=== USER PROMPT (task details) ===",
+        formatTask task
+      ]
diff --git a/Omni/Jr.hs b/Omni/Jr.hs
index c35efa3..b60a029 100755
--- a/Omni/Jr.hs
+++ b/Omni/Jr.hs
@@ -54,6 +54,7 @@ jr
 Usage:
   jr task [<args>...]
   jr work [<task-id>]
+  jr prompt <task-id>
   jr web [--port=PORT]
   jr review [<task-id>] [--auto]
   jr loop [--delay=SECONDS]
@@ -67,6 +68,7 @@ Usage:
 Commands:
   task          Manage tasks
   work          Start a worker agent on a task
+  prompt        Show the system prompt that would be sent to the agent
   web           Start the web UI server
   review        Review a completed task (show diff, accept/reject)
   loop          Run autonomous work+review loop
@@ -94,6 +96,21 @@ move args
             Just p -> fromMaybe Web.defaultPort (readMaybe p)
             Nothing -> Web.defaultPort
       Web.run port
+  | args `Cli.has` Cli.command "prompt" = do
+      case Cli.getArg args (Cli.argument "task-id") of
+        Nothing -> do
+          IO.hPutStrLn IO.stderr "Error: task-id is required"
+          Exit.exitFailure
+        Just tidStr -> do
+          let tid = Text.pack tidStr
+          tasks <- TaskCore.loadTasks
+          case TaskCore.findTask tid tasks of
+            Nothing -> do
+              IO.hPutStrLn IO.stderr ("Error: task not found: " <> tidStr)
+              Exit.exitFailure
+            Just task -> do
+              prompt <- AgentWorker.buildFullPrompt task
+              putText prompt
   | args `Cli.has` Cli.command "work" = do
       -- Always run in current directory
       let path = "."