{
  "schema_version": "1.3.0",
  "slug": "what-structural-signals-indicate-the-sse-resumption-cursor-has-silently-desynchronized-from-the-mcp-session-s-stream-epoch",
  "title": "What structural signals indicate the SSE resumption cursor has silently desynchronized from the MCP session's stream epoch",
  "date_of_record": "2026 November 13",
  "scope": "Applies to MCP servers and clients negotiating the HTTP-native streamable transport (POST for request/response, GET for the server-to-client SSE channel) where the client advertises resumability via `Last-Event-ID`. Does not apply to pure WebSocket transports, nor to single-shot non-resumable SSE where the server never emits `id:` fields.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-the-sse-resumption-cursor-has-silently-desynchronized-from-the-mcp-session-s-stream-epoch.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-the-sse-resumption-cursor-has-silently-desynchronized-from-the-mcp-session-s-stream-epoch.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-structural-signals-indicate-the-sse-resumption-cursor-has-silently-desynchronized-from-the-mcp-session-s-stream-epoch.warrant.json"
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  "token_profile": {
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  "remnant_summary": {
    "core_distinction": "The distinction that matters is between *transport-level resumption* and *session-level stream continuity*. The MCP streamable transport lets a client reconnect its SSE GET channel and present `Last-Event-ID` so the server can replay buffered events. The trap: an `id:` value is a valid integer that the server will happily accept, and the replay will \"succeed...",
    "what_was_observed": "During a long-running tool-call session, the client's SSE GET channel dropped on an idle timeout. The client reconnected with `Last-Event-ID: 8412`. The server returned HTTP 200 and immediately emitted an event with `id: 17`. There was no error frame, no `retry:` hint, no session-termination notice. The client library treated `17` as the next cursor and continued. Subsequent events incremented `17, 18, 19...`. The se...",
    "condition_of_validity": "This diagnosis is valid only when the server's event `id` is specified as monotonically increasing within a session epoch, and the client persists the last seen `id` across reconnects. If the server uses opaque non-numeric IDs, or explicitly documents per-epoch counters with an epoch tag embedded in the ID (e.g., `epoch:seq`), then a bare integer comparison ...",
    "decision_boundary": "The boundary is: **does the client validate cursor monotonicity and epoch identity on the first replayed frame, or does it trust the transport's HTTP 200 as proof of continuity?** - Below the boundary (accept): short-lived sessions where any dropped event is recoverable by re-issuing the originating request, and where the server guarantees buffer lifetime ex...",
    "operational_effect": "Clients that enforce cursor monotonicity convert a silent data-loss failure into an explicit, recoverable session-restart. Clients that do not enforce it exhibit the worst failure class in the transport: a hung tool call with no transport-level error, indistinguishable at the application layer from a slow server. The enforcement cost is one integer compariso..."
  },
  "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": "2af8a02f3a8a967cfa0d86a9af4ef3662dc6fdf0dfe3704d37d070330242ee09",
    "verified_classes": [
      "StreamEpochDesyncError"
    ],
    "verified_functions": [
      "validate_resumed_cursor"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "StreamEpochDesyncError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}