fix(mcp): substitute static error envelope on encode failure instead of writing empty body

CHANGELOG.md

@@ -40,6 +40,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - iCloud sync of app settings (general, appearance, editor, data grid, history, tabs, keyboard, AI) no longer silently does nothing when a category's payload fails to decode. Each of the eight category branches previously wrapped the decode in `try?`, so a record written by a newer schema version would fall through with no log, no error, and no UI signal: the user would think their settings synced when they hadn't. Decode failures now skip the category and log which one failed and why.
 - Keychain reads no longer collapse a cancelled Touch ID prompt, a failed biometric auth, or any unknown OSStatus into "not found". The `KeychainResult` enum now distinguishes `.userCancelled`, `.authFailed`, and `.error(OSStatus)` from `.notFound`, and the read paths in connection passwords, SSH profile secrets, AI provider keys, and the license key log each case with its own message. Previously a cancelled prompt looked identical to a missing entry, so the caller would treat the password as gone and silently re-save with an empty string on the next write, producing duplicate keychain entries or a connection saved with a blank password.
 - Terminal PTY writes retry on `EINTR` instead of treating any non-positive return as "we're done". A signal mid-write previously truncated the input the user typed; the loop would exit silently and the keystrokes were partially sent. The new path retries on `EINTR`, logs the byte position and errno on any other non-recoverable failure, and reports a return value of zero distinctly so the cause is visible in Console.
+- MCP HTTP transport no longer writes an empty body when JSON encoding of the response envelope fails. Five sites in `MCPInboundExchange` and `MCPHttpRequestRouter` previously fell back to `Data()`, sending zero bytes to the client which then saw a protocol violation and either disconnected or hung. The encode-failure paths now log and substitute a static `{"jsonrpc":"2.0","id":null,"error":{"code":-32603,"message":"internal_error"}}` envelope; the pairing-exchange success path falls back to `internalServerError` with a small JSON error body.
 - Result-grid cells on rows marked for deletion keep their dropdown / date / JSON / blob chevron visible at reduced opacity instead of hiding it, so the cell type is still legible while clearly inactive. Click on the dimmed chevron is a no-op; FK arrow navigation is unchanged. Matches the macOS HIG "disabled appearance" guideline.
 - Foreign key navigation from a table with unsaved edits opens the referenced table in a new window tab to preserve the edit buffer. Closing that new tab no longer wipes the original tab's data grid. Previously the new tab's teardown broadcast a connection-scoped event that other coordinators on the same connection received, causing them to release their cell data.
 - Tables sidebar refreshes automatically after a successful SQL import; the refresh notification now fires after the success sheet's dismissal animation, so the main window is key when the observer runs (#1114)

TablePro/Core/MCP/Transport/MCPHttpRequestRouter.swift

@@ -4,6 +4,10 @@ import os
 struct MCPHttpRequestRouter: Sendable {
     private static let logger = Logger(subsystem: "com.TablePro", category: "MCP.HttpRouter")
 
+    private static let staticInternalErrorEnvelope = Data(
+        #"{"jsonrpc":"2.0","id":null,"error":{"code":-32603,"message":"internal_error"}}"#.utf8
+    )
+
     typealias InboundEmitter = @Sendable (MCPInboundExchange) -> AsyncStream<MCPInboundExchange>.Continuation.YieldResult
     typealias SseStarter = @Sendable (UUID, MCPSessionId, HttpConnectionContext) async -> Void
     typealias ResponderSinkFactory = @Sendable (HttpConnectionContext) -> any MCPResponderSink
@@ -115,8 +119,13 @@ struct MCPHttpRequestRouter: Sendable {
             Self.logger.info("Integrations exchange succeeded (token len=\(token.count, privacy: .public))")
             let label = await Self.resolveTokenLabel(for: token)
             MCPAuditLogger.logPairingExchange(outcome: .success, tokenName: label, ip: ip)
-            let payload = (try? JSONEncoder().encode(ExchangeResponse(token: token))) ?? Data()
-            await context.writePlainJsonResponse(status: .ok, body: payload)
+            do {
+                let payload = try JSONEncoder().encode(ExchangeResponse(token: token))
+                await context.writePlainJsonResponse(status: .ok, body: payload)
+            } catch {
+                Self.logger.error("Encode ExchangeResponse failed: \(error.localizedDescription, privacy: .public)")
+                await context.writePlainJsonError(status: .internalServerError, message: "internal_error")
+            }
             await context.cancel()
         case .failure(let error):
             let mapped = Self.mapExchangeError(error)
@@ -422,7 +431,13 @@ struct MCPHttpRequestRouter: Sendable {
         requestId: JsonRpcId?
     ) async {
         let envelope = error.toJsonRpcErrorResponse(id: requestId)
-        let data = (try? JSONEncoder().encode(envelope)) ?? Data()
+        let data: Data
+        do {
+            data = try JSONEncoder().encode(envelope)
+        } catch {
+            Self.logger.error("Encode top-level error envelope failed: \(error.localizedDescription, privacy: .public); using static fallback")
+            data = Self.staticInternalErrorEnvelope
+        }
         await context.writeJsonResponse(
             data: data,
             status: error.httpStatus,

TablePro/Core/MCP/Transport/MCPInboundExchange.swift

@@ -51,6 +51,10 @@ public protocol MCPResponderSink: Sendable {
 public actor MCPExchangeResponder {
     private static let logger = Logger(subsystem: "com.TablePro", category: "MCP.HttpServer")
 
+    private static let staticInternalErrorEnvelope = Data(
+        #"{"jsonrpc":"2.0","id":null,"error":{"code":-32603,"message":"internal_error"}}"#.utf8
+    )
+
     private let sink: MCPResponderSink
     private var completed: Bool = false
     private let requestId: JsonRpcId?
@@ -71,8 +75,14 @@ public actor MCPExchangeResponder {
         do {
             body = try JsonRpcCodec.encode(message)
         } catch {
+            Self.logger.error("Encode response failed: \(error.localizedDescription, privacy: .public)")
             let fallback = MCPProtocolError.internalError(detail: "encode failed").toJsonRpcErrorResponse(id: requestId)
-            body = (try? JSONEncoder().encode(fallback)) ?? Data()
+            do {
+                body = try JSONEncoder().encode(fallback)
+            } catch {
+                Self.logger.error("Encode internal_error envelope failed: \(error.localizedDescription, privacy: .public); using static fallback")
+                body = Self.staticInternalErrorEnvelope
+            }
         }
 
         await sink.writeJson(body, status: .ok, sessionId: sessionId, extraHeaders: [])
@@ -87,7 +97,13 @@ public actor MCPExchangeResponder {
         completed = true
 
         let envelope = error.toJsonRpcErrorResponse(id: responseId ?? requestId)
-        let data = (try? JSONEncoder().encode(envelope)) ?? Data()
+        let data: Data
+        do {
+            data = try JSONEncoder().encode(envelope)
+        } catch {
+            Self.logger.error("Encode error envelope failed: \(error.localizedDescription, privacy: .public); using static fallback")
+            data = Self.staticInternalErrorEnvelope
+        }
         await sink.writeJson(data, status: error.httpStatus, sessionId: nil, extraHeaders: error.extraHeaders)
         await sink.closeConnection()
     }
@@ -138,7 +154,13 @@ public actor MCPExchangeResponder {
         completed = true
 
         let envelope = error.toJsonRpcErrorResponse(id: requestId)
-        let data = (try? JSONEncoder().encode(envelope)) ?? Data()
+        let data: Data
+        do {
+            data = try JSONEncoder().encode(envelope)
+        } catch {
+            Self.logger.error("Encode reject envelope failed: \(error.localizedDescription, privacy: .public); using static fallback")
+            data = Self.staticInternalErrorEnvelope
+        }
         await sink.writeJson(data, status: error.httpStatus, sessionId: nil, extraHeaders: error.extraHeaders)
         await sink.closeConnection()
     }