{
  "schema_version": "1.3.0",
  "slug": "when-must-an-instance-treat-a-resumable-sse-stream-as-dead-rather-than-resumable-the-last-event-id-elicitation-pending-boundary-in-mcp-streamable-http",
  "title": "When must an instance treat a resumable SSE stream as dead rather than resumable: the Last-Event-ID / elicitation-pending boundary in MCP streamable HTTP",
  "date_of_record": "2026 November 8",
  "scope": "Applies to MCP clients and servers using the streamable HTTP transport with SSE streaming, `Last-Event-ID` based resumption, and server-push elicitation requests that are pending across a stream break. Does not apply to stdio transport, to stateless one-shot HTTP request/response usage, or to streams where the server has explicitly signalled session termination.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-an-instance-treat-a-resumable-sse-stream-as-dead-rather-than-resumable-the-last-event-id-elicitation-pending-boundary-in-mcp-streamable-http.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-treat-a-resumable-sse-stream-as-dead-rather-than-resumable-the-last-event-id-elicitation-pending-boundary-in-mcp-streamable-http.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-treat-a-resumable-sse-stream-as-dead-rather-than-resumable-the-last-event-id-elicitation-pending-boundary-in-mcp-streamable-http.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1460,
    "python_slice_tokens": 201,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "A broken SSE connection has two distinct recovery semantics that are routinely conflated by naive clients: *transport resumption* (the client reconnects with `Last-Event-ID` and continues reading the same logical stream) and *session liveness* (the server-side session, its pending server-to-client requests, and its elicitation state still exist and will be h...",
    "what_was_observed": "In a deployment where the server held a pending `elicitation/create` (asking the operator to confirm a destructive tool invocation) and the client's SSE connection dropped due to a load-balancer idle timeout at 60s, the client reconnected with `Last-Event-ID` set to the last successfully processed event, which was the elicitation request event itself. The server, whose replay buffer retained that event, re-sent it. T...",
    "condition_of_validity": "The rule \"reconnect with `Last-Event-ID` and re-process replayed events\" is valid only when all of the following hold: 1. The replayed events are *idempotently processable* — i.e., re-processing an event has no side effect beyond what the first processing did. Progress notifications and log messages satisfy this. Elicitation requests and any request expectin...",
    "decision_boundary": "On reconnect, for each replayed event that is a server-to-client *request* (elicitation, sampling, or any `…/create`-style push): - If the server's replay response includes an explicit liveness assertion for that request (e.g., a fresh request-scoped token, or a cancellation event covering it), process it as live. - If the replayed event's request ID is olde...",
    "operational_effect": "Correctly drawing this boundary converts a silent infinite re-prompt loop (user asked repeatedly, operation never completes, server accumulates orphaned cancellations) into a single, explicit, terminal failure that the agent layer can surface and act on — typically by re-issuing the whole tool invocation under a new session rather than trying to salvage the ..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "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": "3afafc903a5dd75abed04fbc5cf6f128732704d2a8958f3d518fc56ef1784a08",
    "verified_classes": [
      "StaleElicitationError",
      "UnknownPendingRequestError"
    ],
    "verified_functions": [
      "resume_stream_and_reconcile"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "StaleElicitationError",
      "UnknownPendingRequestError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}