fix(session): prevent context overflow by adding safety margin to compaction check

packages/opencode/src/session/compaction.ts

@@ -27,20 +27,21 @@ export namespace SessionCompaction {
     ),
   }
 
+  export const PRUNE_MINIMUM = 20_000
+  export const PRUNE_PROTECT = 40_000
+  export const OVERHEAD_BUFFER = 50_000
+
   export async function isOverflow(input: { tokens: MessageV2.Assistant["tokens"]; model: Provider.Model }) {
     const config = await Config.get()
     if (config.compaction?.auto === false) return false
     const context = input.model.limit.context
     if (context === 0) return false
     const count = input.tokens.input + input.tokens.cache.read + input.tokens.output
     const output = Math.min(input.model.limit.output, SessionPrompt.OUTPUT_TOKEN_MAX) || SessionPrompt.OUTPUT_TOKEN_MAX
-    const usable = context - output
+    const usable = context - output - OVERHEAD_BUFFER
     return count > usable
   }
 
-  export const PRUNE_MINIMUM = 20_000
-  export const PRUNE_PROTECT = 40_000
-
   const PRUNE_PROTECTED_TOOLS = ["skill"]
 
   // goes backwards through parts until there are 40_000 tokens worth of tool

packages/opencode/src/session/prompt.ts

@@ -773,12 +773,17 @@ export namespace SessionPrompt {
           // Add support for other types if needed
         }
 
+        const text = textParts.join("\n\n")
+        const output = text.length > 30_000
+          ? text.slice(0, 30_000) + `\n\n[MCP output truncated: exceeded 30000 char limit]`
+          : text
+
         return {
           title: "",
           metadata: result.metadata ?? {},
-          output: textParts.join("\n\n"),
+          output,
           attachments,
-          content: result.content, // directly return content to preserve ordering when outputting to model
+          content: result.content,
         }
       }
       item.toModelOutput = (result) => {

packages/opencode/src/tool/webfetch.ts

@@ -87,53 +87,19 @@ export const WebFetchTool = Tool.define("webfetch", {
     const contentType = response.headers.get("content-type") || ""
 
     const title = `${params.url} (${contentType})`
+    const isHtml = contentType.includes("text/html")
 
-    // Handle content based on requested format and actual content type
-    switch (params.format) {
-      case "markdown":
-        if (contentType.includes("text/html")) {
-          const markdown = convertHTMLToMarkdown(content)
-          return {
-            output: markdown,
-            title,
-            metadata: {},
-          }
-        }
-        return {
-          output: content,
-          title,
-          metadata: {},
-        }
+    const raw = params.format === "markdown" && isHtml
+      ? convertHTMLToMarkdown(content)
+      : params.format === "text" && isHtml
+        ? await extractTextFromHTML(content)
+        : content
 
-      case "text":
-        if (contentType.includes("text/html")) {
-          const text = await extractTextFromHTML(content)
-          return {
-            output: text,
-            title,
-            metadata: {},
-          }
-        }
-        return {
-          output: content,
-          title,
-          metadata: {},
-        }
+    const output = raw.length > 30_000
+      ? raw.slice(0, 30_000) + `\n\n[Output truncated: exceeded 30000 char limit]`
+      : raw
 
-      case "html":
-        return {
-          output: content,
-          title,
-          metadata: {},
-        }
-
-      default:
-        return {
-          output: content,
-          title,
-          metadata: {},
-        }
-    }
+    return { output, title, metadata: {} }
   },
 })