{
  "schema_version": "1.3.0",
  "slug": "why-does-an-instance-of-an-mcp-http-streaming-server-silently-degrade-to-non-streaming-behavior-after-a-capability-renegotiation",
  "title": "Why does an instance of an MCP HTTP streaming server silently degrade to non-streaming behavior after a capability renegotiation",
  "date_of_record": "2026 November 14",
  "scope": "Applies to MCP servers exposing tools over HTTP with server-sent-event (SSE) streaming, where the client may re-send an `initialize` request or send a `notifications/initialized` after a transport reconnect. Does not apply to stdio transports, nor to servers that reject all post-initialize `initialize` frames unconditionally.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/why-does-an-instance-of-an-mcp-http-streaming-server-silently-degrade-to-non-streaming-behavior-after-a-capability-renegotiation.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-of-an-mcp-http-streaming-server-silently-degrade-to-non-streaming-behavior-after-a-capability-renegotiation.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/why-does-an-instance-of-an-mcp-http-streaming-server-silently-degrade-to-non-streaming-behavior-after-a-capability-renegotiation.warrant.json"
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  "token_profile": {
    "full_markdown_tokens": 1568,
    "python_slice_tokens": 284,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The failure mode is not \"the stream broke.\" The failure mode is that the server accepted a *second* `initialize` handshake whose declared `capabilities` were a subset of the first, and then—correctly per the spec, incorrectly per operator intent—narrowed its own advertised tool-streaming surface for the remainder of the connection. The distinction that matte...",
    "what_was_observed": "A long-lived client (an agent runtime) reconnected its HTTP transport after a 502 from a load balancer. The reconnect logic replayed the full handshake: `initialize` → `notifications/initialized`. The replayed `initialize` was constructed by a code path that had defaulted `capabilities.tools.streaming` to `false` because the flag was read from a config object that had been reset during the reconnect. The server: 1. A...",
    "condition_of_validity": "This record is valid when all of the following hold: - The transport is HTTP (not stdio) and the server supports SSE for tool results. - The server keys session state by a header (e.g., `Mcp-Session-Id`) and permits `initialize` on an existing session rather than rejecting it with a protocol error. - The server derives per-session streaming behavior from the...",
    "decision_boundary": "The operator-facing decision is whether to treat a post-reconnect `initialize` as advisory or authoritative. - **Treat as authoritative (spec-literal):** the server must honor the new capability set. This is correct and produces this failure mode. It is the right choice only if the client is guaranteed to re-send a complete, validated handshake—which reconne...",
    "operational_effect": "The downstream effect is the dangerous part: silent degradation produces *plausible* results, not errors. An empty tool result is indistinguishable, to a reasoning agent, from a tool that legitimately returned nothing. The agent proceeds, and the failure surfaces much later as a wrong answer with no traceable cause. Monitoring on HTTP status codes and JSON-R..."
  },
  "matched_failure_symptoms": [
    "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": "c71b384440033ff477990affb71f571b6d27d55b5782bf6a14ee04b9bb032729",
    "verified_classes": [
      "CapabilityRenegotiationError"
    ],
    "verified_functions": [
      "validate_reinitialize",
      "handle_initialize"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 3,
    "raised_exceptions": [
      "CapabilityRenegotiationError"
    ],
    "sample_fail_closed_invariants": [
      "re-initialize received without a session identifier; cannot determine whether this is a new or existing session"
    ],
    "stdlib_dependencies": [],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}