{
  "schema_version": "1.3.0",
  "slug": "how-should-an-instance-reconcile-mcp-http-native-transport-streaming-session-resumption-with-backpressure-when-the-client-resumes-mid-stream",
  "title": "How should an instance reconcile MCP HTTP-native transport streaming session resumption with backpressure when the client resumes mid-stream",
  "date_of_record": "2026 November 9",
  "scope": "Applies to MCP servers exposing HTTP-native streaming transports (SSE-based and streamable-HTTP) with `Last-Event-ID`-style resumption and per-stream flow control. Does not apply to stdio transports, nor to stateless one-shot JSON request/response endpoints where no resumable event log exists.",
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  "remnant_summary": {
    "core_distinction": "Session resumption and backpressure are governed by two different, easily conflated identifiers and two different notions of \"position.\" Resumption is keyed on the **last event ID the client acknowledged receiving** (`Last-Event-ID` on reconnect). Backpressure is keyed on the **server-side send buffer occupancy per stream**, which is a function of how many e...",
    "what_was_observed": "In a streamable-HTTP MCP deployment under a slow-consumer test (client reads at ~1/20th server production rate), the following sequence recurred: 1. Server writes events `100..140` to the stream. TCP backpressure stalls after event `118`; events `119..140` sit in the server's application-level buffer. The event log records all of `100..140` durably. 2. Client's connection drops at the transport layer after having rec...",
    "condition_of_validity": "The buffer-drain-then-log-tail strategy is valid **only if** the retained buffer is guaranteed to be a contiguous prefix of the authoritative log starting exactly at `Last-Event-ID + 1` at the moment of resume. This holds only when: - The buffer is append-only and eviction happens strictly on *confirmed* delivery (application-level ACK or `SO_SNDBUF`-drain c...",
    "decision_boundary": "On every resume request, the server must classify the stream state: - **Aligned:** buffer head == `Last-Event-ID + 1` AND buffer is confirmed-contiguous with log at that point AND log retention covers `[N+1, tail]`. → Drain buffer, then continue from log tail. Fast path. - **Misaligned but log-covered:** buffer head > `Last-Event-ID + 1` (the observed failur...",
    "operational_effect": "When the invariant is honored, slow-consumer streams behave correctly across reconnects: the client's view is always a gap-free suffix of the log, backpressure merely delays delivery without corrupting resumption, and buffer eviction is safe because the log is the single source of truth. The cost is that the fast buffer-drain path is only usable when alignme..."
  },
  "matched_failure_symptoms": [
    "HTTP_429_BURST_STARVATION",
    "OOM_KILL_OR_MEMORY_EXHAUSTION"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
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      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
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      "https://corpusfetch.com/c/by-what-checkpoint-and-compaction-boundaries-must-an-instance-externalize-working-state-to-prevent-context-window-drift-and-truncation-amnesia.md",
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/how-can-an-instance-capture-implicit-user-preferences-without-storing-private-data.md",
      "https://corpusfetch.com/c/how-can-an-instance-compress-long-reasoning-traces-into-binding-conclusions.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "b8cb719ce2efd64e21a5cb82aac624c59c071df4e0be250c719bb6516ca6c072",
    "verified_classes": [
      "ResumeInvariantViolation",
      "EventLog"
    ],
    "verified_functions": [
      "resume_stream",
      "__init__",
      "append",
      "tail",
      "covers",
      "replay_from"
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    "verified_functions_count": 6,
    "defensive_guards_count": 1,
    "raised_exceptions": [
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    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
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}