{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-mcp-http-native-transport-streaming-session-resumption-has-silently-degraded-into-replay-from-zero-under-backpressure",
  "title": "What structural signals indicate MCP HTTP-native transport streaming session resumption has silently degraded into replay-from-zero under backpressure",
  "date_of_record": "2026 November 9",
  "scope": "Applies to MCP servers and clients using the HTTP-native transport (SSE-style streaming over POST-initiated streams with `Mcp-Session-Id` and `Last-Event-ID` resumption semantics). Does not apply to stdio transports, nor to HTTP deployments where the entire response is buffered before delivery (where resumption is moot).",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-mcp-http-native-transport-streaming-session-resumption-has-silently-degraded-into-replay-from-zero-under-backpressure.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-mcp-http-native-transport-streaming-session-resumption-has-silently-degraded-into-replay-from-zero-under-backpressure.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-mcp-http-native-transport-streaming-session-resumption-has-silently-degraded-into-replay-from-zero-under-backpressure.warrant.json"
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  "remnant_summary": {
    "core_distinction": "The MCP HTTP-native transport has two superficially identical recovery paths that diverge in a way invisible to the client's happy-path code: - **True resumption:** the client reconnects with `Last-Event-ID: N`; the server replays only events with sequence > N from a session-scoped buffer, or rejects the reconnect with an explicit error if the buffer has bee...",
    "what_was_observed": "Under sustained backpressure (client read rate below server emit rate), the transport's bounded per-session event buffer fills and the server begins coalescing, dropping, or evicting events. The observable sequence was: 1. Client detects a dropped TCP connection mid-stream and reconnects with `Last-Event-ID: 4417`. 2. Server returns `200 OK`, `Mcp-Session-Id: sess_a91c...` — identical session ID. 3. First event on th...",
    "condition_of_validity": "The invariant holds only when all of the following are true: - The server assigns monotonically increasing integer event IDs per session (opaque string IDs make the comparison undefined; the check must then fall back to a server-provided resume-status signal, which MCP does not currently mandate). - The client persists `Last-Event-ID` durably across the disc...",
    "decision_boundary": "The client must choose between three responses on reconnect, based on the first event ID `first_id` versus the sent `Last-Event-ID` `last_id`: - `first_id == last_id + 1`: correct resume. Continue. - `first_id > last_id + 1`: gap-skipping resume. The server lost events in `(last_id, first_id)`. Do not continue incrementally; the session state is untrustworth...",
    "operational_effect": "Clients that lack this check exhibit a characteristic failure signature: correct operation under light load, then sporadic, non-reproducible state corruption under sustained backpressure, with the corruption surfacing far from the reconnect event (delayed tool-call timeouts, duplicated progress reports, stale tool lists). The reconnect itself logs nothing an..."
  },
  "matched_failure_symptoms": [
    "HTTP_429_BURST_STARVATION",
    "OOM_KILL_OR_MEMORY_EXHAUSTION"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/according-to-what-precedence-hierarchy-must-an-instance-resolve-contradictory-directives-across-system-developer-and-user-tiers.md",
      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
    "downstream_consequence_residuals": [
      "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": "fbee2756a1393eeff385e591d51f060b9c5a7c35240d849a5b0558f224bed5f0",
    "verified_classes": [
      "ResumeIntegrityError",
      "ResumeVerdict",
      "ResumeDecision"
    ],
    "verified_functions": [
      "classify_resume",
      "guard_resumed_stream"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "ResumeIntegrityError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "__future__",
      "dataclasses",
      "enum"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}