{
  "schema_version": "1.3.0",
  "slug": "what-backpressure-invariants-must-survive-when-the-queue-itself-is-the-bottleneck",
  "title": "What backpressure invariants must survive when the queue itself is the bottleneck?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** The queue's own operations can become the bottleneck, and the application producers/consumers alone are insufficient indicators of system health. * **Does not apply when:** The queue is verifiably over-provisioned (dedic",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/what-backpressure-invariants-must-survive-when-the-queue-itself-is-the-bottleneck.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/what-backpressure-invariants-must-survive-when-the-queue-itself-is-the-bottleneck.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/what-backpressure-invariants-must-survive-when-the-queue-itself-is-the-bottleneck.warrant.json"
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  "remnant_summary": {
    "core_distinction": "The separation between **application-level backpressure** (the producer and consumer negotiate rate) and **queue-level backpressure** (the queue itself is saturated and cannot accept enqueues or serve dequeues). Relying on application-level backpressure creates the **Queue Saturation Blindspot**: the producer and consumer appear healthy, each doing their par...",
    "what_was_observed": "In queue-mediated agent architectures, failing to detect queue-level saturation produces three primary failure modes: 1. **Silent Message Loss:** The queue drops messages due to disk pressure or replication lag, but the producer sees `ACK` and believes the message was durable. 2. **Consumer Starvation:** Consumers appear busy but are actually blocked waiting for the queue to serve messages. The queue's dequeue throug...",
    "condition_of_validity": "* **Applies when:** The queue's own operations can become the bottleneck, and the application producers/consumers alone are insufficient indicators of system health. * **Does not apply when:** The queue is verifiably over-provisioned (dedicated capacity, unlimited disk, replication with headroom), or the agent does not use a queue.",
    "decision_boundary": "1. **Is `queue_lag_signature` increasing over time?** If yes, the queue is falling behind. Apply backpressure to producers or scale consumers. 2. **Does `queue_disk_pressure_receipt` show utilization above the safe threshold (e.g., 80%)?** If yes, the queue may drop messages or reject enqueues. Stop producing until disk recovers. 3. **Does `enqueue_ack_durab...",
    "operational_effect": "1. **Queue Health Awareness:** Detects queue-level bottlenecks that application-level monitoring misses. 2. **Producer-Side Protection:** Halts production before the queue drops messages, allowing graceful recovery. 3. **Durability Transparency:** Distinguishes provisional ACKs from durable ACKs, preventing false confidence in message persistence."
  },
  "matched_failure_symptoms": [
    "HTTP_429_BURST_STARVATION"
  ],
  "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": "fc934a668e46221dbe9d0fd5fbcb36861ab7e94c18a0c7fce9269d6897d7043f",
    "verified_classes": [
      "QueueVerdict",
      "QueueState",
      "QueuePolicy",
      "QueueManifest",
      "QueueSaturationGuard"
    ],
    "verified_functions": [
      "_hash",
      "evaluate_queue"
    ],
    "verified_functions_count": 2,
    "defensive_guards_count": 0,
    "raised_exceptions": [],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "enum",
      "hashlib",
      "json"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}