Constrain structured planning responses

1 files changed, 13 insertions, 3 deletions

diff --git a/src/Agent.Core/Runtime/PlannerService.cs b/src/Agent.Core/Runtime/PlannerService.cs
index b5ac80e..2a006f7 100644
--- a/src/Agent.Core/Runtime/PlannerService.cs
+++ b/src/Agent.Core/Runtime/PlannerService.cs
@@ -229,25 +229,34 @@ public sealed class PlannerService(IOllamaClient ollama, AgentRuntimeSettings se
         Action<string, IReadOnlyList<OllamaMessage>, OllamaResult?, Exception?>? observeAttempt, Func<PlanResult, TaskGraph> buildGraph, CancellationToken cancellationToken)
     {
         Exception? firstFailure = null;
+        IReadOnlyList<OllamaMessage> attemptMessages = messages;
         for (int attempt = 0; attempt < 2; attempt++)
         {
             OllamaResult? result = null;
             try
             {
                 bool? thinkOverride = attempt == 0 ? null : false;
-                result = await _ollama.ChatStructuredAsync(messages, temperature, PlanSchema.Element, thinkOverride, cancellationToken).ConfigureAwait(false);
+                result = await _ollama.ChatStructuredAsync(attemptMessages, temperature, PlanSchema.Element, thinkOverride, cancellationToken).ConfigureAwait(false);
                 PlanResult? plan = ParsePlan(result.Content);
                 if (plan is null || plan.Tasks.Count == 0)
                     throw new PlannerValidationException("Ollama returned an empty or invalid structured plan.");
                 TaskGraph graph = buildGraph(plan);
-                observeAttempt?.Invoke(phase, messages, result, null);
+                observeAttempt?.Invoke(phase, attemptMessages, result, null);
                 return graph;
             }
             catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested) { throw; }
             catch (Exception ex) when (ex is not (OutOfMemoryException or StackOverflowException or AccessViolationException))
             {
-                observeAttempt?.Invoke(phase, messages, result, ex);
+                observeAttempt?.Invoke(phase, attemptMessages, result, ex);
                 firstFailure ??= ex;
+                if (attempt == 0)
+                {
+                    attemptMessages = messages.Concat([
+                        new OllamaMessage("system",
+                            "The previous response was not a valid TaskGraph JSON object. Do not call or execute any Tool while planning. " +
+                            "Return only one JSON object that matches the supplied schema, beginning with {\"tasks\":[ and containing no Markdown or commentary.")
+                    ]).ToArray();
+                }
             }
         }
         throw new PlannerValidationException($"Structured {phase} failed after think=false retry: {firstFailure?.Message}");
@@ -294,6 +303,7 @@ public sealed class PlannerService(IOllamaClient ollama, AgentRuntimeSettings se
     private static string BuildPlanningInstruction() =>
         """
         You are a Task Planner. Decompose the user request into a TaskGraph of 1-32 tasks.
+        Planning is read-only: do not call or execute Tools. Return only one JSON object matching the supplied schema, with no Markdown or commentary.
         Each task must have:
         - description: a clear, self-contained sub-task description
         - dependencies: array of task indices (0-based) that must complete before this task