fix(github): handle non-JSON upstream tool responses

[tlgimenes]

Summary

• Fix get_file_contents (and other tools) failing when the upstream GitHub MCP server returns plain text instead of JSON
• Previously, non-JSON responses like "successfully downloaded text file (SHA: ...)" caused a Failed to parse error
• Now returns the raw text message when JSON parsing fails, instead of throwing

Test plan

• Call get_file_contents on a text file and verify it returns content without error
• Call tools that return JSON responses and verify they still work correctly

🤖 Generated with Claude Code

---

Summary by cubic

Handle non-JSON responses from the upstream GitHub MCP server so tools like get_file_contents don’t fail on plain-text messages. Added debug logging of upstream callTool results to help trace response formats.

• Bug Fixes
  • Parse JSON when available; otherwise return the original text (or null) instead of throwing.
  • Log upstream callTool responses (tool name and payload) to diagnose non-JSON cases.

^{Written for commit 58eae94. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="github/server/lib/mcp-proxy.ts">

<violation number="1" location="github/server/lib/mcp-proxy.ts:188">
P2: Valid falsy JSON values are misclassified as parse failures because of a truthiness check.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

2 issues found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="github/server/lib/mcp-proxy.ts">

<violation number="1">
P1: Non-JSON tool responses still throw `Failed to parse` instead of falling back to raw text/null.</violation>

<violation number="2" location="github/server/lib/mcp-proxy.ts:171">
P2: Avoid logging full upstream tool results in production; this can expose sensitive payload data and create noisy/large logs.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P1: Non-JSON tool responses still throw Failed to parse instead of falling back to raw text/null.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At github/server/lib/mcp-proxy.ts, line 189:

<comment>Non-JSON tool responses still throw `Failed to parse` instead of falling back to raw text/null.</comment>

<file context>
@@ -185,11 +186,10 @@ export function buildUpstreamTools(
           const parsed = safeJsonParse(msg);
-          if (parsed) {
-            return parsed;
+          if (!parsed) {
+            throw new Error(`Failed to parse: ${msg}`);
           }
</file context>

[cubic-dev-ai]

P2: Avoid logging full upstream tool results in production; this can expose sensitive payload data and create noisy/large logs.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At github/server/lib/mcp-proxy.ts, line 171:

<comment>Avoid logging full upstream tool results in production; this can expose sensitive payload data and create noisy/large logs.</comment>

<file context>
@@ -168,6 +168,7 @@ export function buildUpstreamTools(
             name: toolDef.name,
             arguments: context as Record<string, unknown>,
           });
+          console.log(`[mcp-proxy] callTool result for ${toolDef.name}:`, JSON.stringify(result, null, 2));
           const contents = result.content as
             | Array<{ type: string; text?: string }>
</file context>

Suggested change

	console.log(`[mcp-proxy] callTool result for ${toolDef.name}:`, JSON.stringify(result, null, 2));
	if ((ctx as AppContext<Env>).env.NODE_ENV !== "production") {
	console.log(`[mcp-proxy] callTool result for ${toolDef.name}:`, JSON.stringify(result, null, 2));
	}