{
  "schema_version": "1.3.0",
  "slug": "when-must-a-raft-leader-refuse-to-serve-reads-after-losing-lease-quorum",
  "title": "When must a Raft leader refuse to serve reads after losing lease quorum?",
  "date_of_record": "2026 November 14",
  "scope": "Applies to Raft (and Raft-derived) clusters serving linearizable reads via leader leases or ReadIndex, where the leader may be partitioned from a quorum but still reachable by clients. Does not apply to leader-election safety itself (which remains correct); it concerns the read-path liveness/safety boundary during the window between lease expiry and step-down.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-a-raft-leader-refuse-to-serve-reads-after-losing-lease-quorum.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-a-raft-leader-refuse-to-serve-reads-after-losing-lease-quorum.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-a-raft-leader-refuse-to-serve-reads-after-losing-lease-quorum.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1142,
    "python_slice_tokens": 167,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The distinction is between *holding leadership* and *holding a valid lease*. A Raft leader retains the `leader` role in its local state machine until it observes a higher term or a quorum-backed step-down. During a network partition where the leader is isolated from the majority, the leader's local term does not advance, and it will continue to answer client...",
    "what_was_observed": "In a five-node cluster (Raft, 500 ms heartbeat, 1.5 s election timeout, leader lease of 2 s), a partition isolated the leader L with two followers. Clients pinned to L continued to receive successful linearizable reads for approximately 1.8 s after the majority partition elected a new leader L' and committed a configuration-changing write. The isolated leader's lease had not yet expired by its own clock, and its Read...",
    "condition_of_validity": "The refusal rule is valid — and the stale-read hazard exists — only when all of the following hold: 1. Reads are served as *linearizable* (not stale/bounded-staleness reads, which are exempt by contract). 2. The leader uses a time-based lease derived from a *local* monotonic clock, not a quorum-acknowledged timestamp per read. 3. The client's session does no...",
    "decision_boundary": "The leader must refuse (return `NotLeader` / redirect) a linearizable read when **any** of these is true at request admission: - `now - lastQuorumAckTime > leaseDuration - maxClockSkew`. - The in-flight ReadIndex heartbeat quorum has not acknowledged within `readDeadline`, where `readDeadline < electionTimeout - maxClockSkew`. - A `CheckQuorum` probe in the ...",
    "operational_effect": "Enforcing per-read lease validation converts a silent linearizability violation into a bounded, visible availability dip: clients on the isolated leader receive `NotLeader` redirects within one read-deadline (≈ 300–500 ms) instead of stale data for up to a full lease. The cost is that legitimate reads during transient heartbeat jitter are rejected and must r..."
  },
  "matched_failure_symptoms": [
    "SPLIT_BRAIN_OR_ZOMBIE_WORKER"
  ],
  "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": "46b4d1ac1a48366197646b8ca35dcee235670dea636f95581992aabbc75a05a3",
    "verified_classes": [
      "StaleReadRefused",
      "LeaderReadGate"
    ],
    "verified_functions": [
      "serve_read",
      "_lease_margin_ok",
      "admit_linearizable_read"
    ],
    "verified_functions_count": 3,
    "defensive_guards_count": 2,
    "raised_exceptions": [
      "StaleReadRefused"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "time"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}