fix: prevent ArgumentOutOfRange on agentic string truncation

src/ContextMemory.Core/Agentic/AgentContextCompactor.cs

@@ -66,7 +66,11 @@ public AgentContextCompactor(
         if (estimated <= maxTokens || messages.Count < 4)
             return null;
 
-        var historyId = $"history:{sessionId}:{iteration}:{Guid.NewGuid():N}"[..64];
+        // Keep under common FS/DB id limits without assuming the prefix is already >= 64 chars
+        // (short session ids like Jira keys produced ArgumentOutOfRange on ..[64]).
+        var historyId = $"history:{sessionId}:{iteration}:{Guid.NewGuid():N}";
+        if (historyId.Length > 64)
+            historyId = historyId[..64];
         var transcript = SerializeTranscript(messages);
 
         try

src/ContextMemory.Core/Agentic/Prompts/AgenticToolObservationFormatter.cs

@@ -57,7 +57,9 @@ internal static string TruncateWithPointer(
             return string.IsNullOrWhiteSpace(artifactId) ? payload : payload + pointer;
         }
 
-        var previewLen = Math.Max(64, Math.Min(maxChars - 120, maxChars));
+        // previewLen must never exceed payload.Length (maxChars can be < 64 + pointer overhead).
+        var previewLen = Math.Clamp(maxChars - 120, 1, payload.Length);
+        previewLen = Math.Min(previewLen, Math.Max(1, payload.Length - 1));
         var preview = payload[..previewLen];
         return preview
                + $"\n\n…[truncated {payload.Length - previewLen} chars; artifactId={id} "

src/ContextMemory.Core/Agentic/SessionDiscoveryTools.cs

@@ -188,6 +188,7 @@ public static string ShortenDescription(string? description, int maxChars = 120)
         if (trimmed.Length <= maxChars)
             return trimmed + " (tool_describe for full schema)";
 
-        return trimmed[..Math.Max(40, maxChars - 32)].TrimEnd() + "… (tool_describe for full schema)";
+        var keep = Math.Clamp(maxChars - 32, 1, trimmed.Length);
+        return trimmed[..keep].TrimEnd() + "… (tool_describe for full schema)";
     }
 }

src/ContextMemory.Core/Session/SessionWikiCompiler.cs

@@ -123,7 +123,8 @@ public static WikiCompileResult Compile(
                 if (sb.Length > 0)
                     sb.Append("\n\n");
                 sb.Append(header);
-                sb.Append(body[..availableForBody].TrimEnd());
+                var take = Math.Min(availableForBody, body.Length);
+                sb.Append(body[..take].TrimEnd());
                 sb.Append(PageTruncatedSuffix);
                 remaining = 0;
                 included++;