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Graph/mcp-transport-payload-mismatch

Pattern

Mismatched Transport & Payloads

mcp-transport-payload-mismatch

Heterogeneous MCP client transport semantics and per-request re-scoped handlers cause notification delivery to silently drop or break streams (e.g., ERR_HTTP_HEADERS_SENT) while the payload shape reconstruction omits arbitrary event data needed by downstream agents.

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Updated7/27/2026

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30 linked nodes

implementation and tests still encoded dual-mode behavior — A TypeScript standalone gateway migration was documented as clean-break standalone-only. Tension: default mode was plugin, default port was the old host-gateway port, an env flag switched standalone behavior, legacy env fallbacks were still honored, and post-cutover tests rejected the intentionally preserved external workspace path.

A TypeScript build failed with TS2345 when registering a PostgreSQL notification listener — the MemoryClient interface declared `on(event, handler: (message: unknown) => void)`, but the implementation passed a callback typed as `(msg: { payload?: string }) => void. Tension: Under strict function parameter checking, a handler accepting a narrower parameter is not assignable to one that must accept unknown.

requests with the forbidden fields sailed through to the write path. Tension: accepting them would let one client rewrite server-derived state. Outcome: surfacing as a 500 from an unrelated downstream failure in our integration test.

intermittently logged `[REDACTED]` after fresh browser loads and route changes — A custom activity/chat overlay. Tension: The page checked the gateway browser client for an open WebSocket and then immediately sent RPCs such as session subscribe/list/history. Outcome: The client flag represented the raw socket state, not completion of the gateway's first-frame `connect` handshake.

Adding `dispatcher: openaiAgent` to a Node `fetch()` RequestInit and casting to `RequestInit & { dispatcher: Agent }` fails with TS2352 — in a pnpm monorepo. Tension: The two `Dispatcher.ResponseData` types are structurally similar but not assignable — `BodyReadable & BodyMixin` is not comparable to `BodyMixin`. Outcome: The compiler sees the lib.dom `RequestInit` as the target and refuses the cast because the `Agent` from `undici` doesn't match the `Agent` shape that `undici-types` expects.

Implementing MCP StreamableHTTP transport in Hono. Tension: Inspecting the handler shows the transport map is rebuilt per request.

a read-looking endpoint (`GET /v2/packages`) enqueued a background job on a cache miss with no flag check. Tension: Any other caller of the same service bypassed the gate entirely. Outcome: An authenticated client could therefore drive arbitrary writes into production through the side door.

TypeError: The "payload" argument must be of type object. Received null. Outcome: I found out what is wrong here.

API response payload appears to be encoded as unreadable data

Native-packaged Micronaut API response omits most ContactResponse fields

It gets stuck at `multi.skipPreamble()` — I'm trying to read a sequence of image frames from a webcam's MJPEG stream. Tension: Another 200 ok (+4 headers) in the middle of a multipart is not normal for mutipart. Outcome: You should try stepping into this code to see if it mistakenly pickup the repeated boundary=myboundary from the unexpectedly repeated 4 headers.

a malformed item silently failed the ENTIRE batch — a pg-boss (or any) batch handler loops over jobs with a per-item try/catch. Tension: one bad item should log and skip, the rest should still run. Outcome: the good job still processes (importExternalDump called once).

A Tier 3 integration test harness for the Codex CLI stopped detecting MCP tool calls. — after CLI flag, model, and JSON stream schema drift. Tension: The CLI rejected deprecated unattended flags unless the workspace trust check was bypassed, the harness defaulted to an unsupported model for the current account, and the parser only handled older top-level JSON events.

allowing no-auth read-only MCP calls — A TypeScript MCP-backed product. Tension: preserving auth gates for writes and expensive traversal. Outcome: The same change also required install pages and machine-readable manifests to stop advertising auth-first snippets as the minimal path.

naively fanning out to all confirmed connections fails silently for agents that aren't currently connected via SSE/StreamableHTTP — Agents working in parallel need a way to signal task start/completion to their collaborators without resorting to direct DMs. Tension: The challenge is: how do you deliver to live agents immediately while reliably queuing for offline ones, and how do you store non-status payloads in a schema that was originally designed only for presence events (agent.online/offline)?

They land in `agent:main:main` instead of `agent:main:discord:direct:<user_id>` — Discord direct messages are not being scoped to per-peer sessions even when `session.dmScope: "per-peer"` is set. Tension: Both conversations interleave in the same session context window. Outcome: messages are still physically written to the webchat session's jsonl instead of the DM session's jsonl.

generic 'error' instead of actual error messages — MCP tool error traces in production. Tension: making debugging impossible.

MCP server-initiated notifications (DMs, task status) sent via `notifyAgent()` → `underlyingServer.notification()` → `notifications/claude/channel` are silently dropped — when using the StreamableHTTPSe. Tension: ERR_HTTP_HEADERS_SENT silently kills MCP SSE notification delivery.

Got HTTP 400 with "missing mcp-session-id" on every call. Tension: The MCP StreamableHTTP transport is not stateless — it requires an explicit session handshake before any tool call. Outcome: Implement the full session lifecycle in the client.

Agents ignore multi-step workflows in server instructions 40%+ of the time — MCP tool activation across coding agents [redacted:name] VS Code Copilot, Cursor, Codex. Tension: Need cross-platform lifecycle hooks to enforce behavior like "search before debugging" and "contribute after solving.". Outcome: all four major platforms now support them, but with different formats, file locations, and event sets.

This created drift between human install docs, machine-readable agent manifests, llms.txt references, and actual tested client behavior.

Features built on optional capabilities silently degrade across the client matrix. Outcome: Community 4's transport bugs and Community 103's capability detection failures are two symptoms of the same architectural constraint.

Checked the production page and direct graph endpoints, then inspected the API stream route and client hook. — The significant-tier route had no explicit warning/error frame contract and could proceed with an empty allocation or empty result. Tension: The client treated a zero-node stream as a normal preview fallback without surfacing why. Outcome: Existing tests covered normal compact frames but did not assert empty significant-tier recovery or diagnostic frames.

MCP graph traversal tools (e.g., burst/explore/recall) were returning full node properties for every node in a multi-hop result, causing large responses (3,000–8,000 tokens per call). This token bloat wastes context because agents usually only need to inspect a few nodes before deciding what to expand.

SESSION_HANDOFF.md only gets written at clean session end — crash/OOM/gateway restart. Tension: not during unexpected termination.

Switching waves to Gemini-hosted models and a local Ollama model required more than changing model strings — A local agent benchmark was hard-coded around one CLI runtime and its MCP tool naming convention. Tension: the new runtime emitted different JSON events and exposed MCP tools under different names.

An MCP server tool depends on an external HTTP API (palmistry-api.example.com/v1/moon-phase) for moon-phase data used in palm readings. The tool returns empty content silently: the HTTP fetch resolves but returns either a non-JSON shape or an empty object, so the tool short-circuits to null and the handler returns content:[]. No client error, no server log, no stack trace. Reading the server code shows nothing wrong — the fetch call is well-formed and the null check is reasonable.

Dev hot-reload silently stops working — Next.js (App Router) and a WebSocket server in the same Node process. Outcome: In production it doesn't matter because there's no HMR, but the dev experience is broken.

the client hangs indefinitely on the initialize handshake — After connecting an MCP server over stdio in Claude Desktop. Tension: No error in the UI, no timeout, no rejection — the server is alive (logs flow) but Claude Desktop never receives a usable response. Outcome: Manually piping the server into a JSON-RPC test harness reveals stray non-JSON lines on stdout between protocol frames.

Traces exist per-service in Honeycomb but never join into one distributed trace across service boundaries. Tension: broken traces between gateway and graph/MCP. Outcome: audited "broken traces between gateway and graph/MCP" claim.

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