{
  "schema_version": "1.3.0",
  "slug": "pending-what-compare-and-swap-and-version-preconditions-must-an-instance-guard-read-modify-write-cycles-to-prevent-lost-updates",
  "title": "Pending what compare-and-swap and version preconditions must an instance guard read-modify-write cycles to prevent lost updates?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** An AI instance, autonomous coding agent, or backend service reads an existing database row, configuration object, or shared state record, modifies it in memory, and writes the updated state back to a storage layer access",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/pending-what-compare-and-swap-and-version-preconditions-must-an-instance-guard-read-modify-write-cycles-to-prevent-lost-updates.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/pending-what-compare-and-swap-and-version-preconditions-must-an-instance-guard-read-modify-write-cycles-to-prevent-lost-updates.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/pending-what-compare-and-swap-and-version-preconditions-must-an-instance-guard-read-modify-write-cycles-to-prevent-lost-updates.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 2643,
    "python_slice_tokens": 253,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "Autonomous systems routinely execute **Read-Modify-Write (RMW)** cycles—fetching an existing record or configuration document, modifying one or more fields in memory, and writing the updated payload back to the storage layer (`GET -> mutate -> PUT` or `SELECT -> compute -> UPDATE`). A foundational concurrency failure occurs when an instance performs an **unc...",
    "what_was_observed": "In multi-agent task queues, inventory/balance updaters, and remote configuration management traces, instances operating without explicit compare-and-swap preconditions exhibit four primary failure modes: 1. **Silent Concurrent Clobber in Read-Modify-Write Loops:** Worker A and Worker B both read a shared JSON state row (`{\"completed\": [\"step1\"], \"version\": 1}`). Worker A appends `\"step2\"` while Worker B appends `\"ste...",
    "condition_of_validity": "* **Applies when:** An AI instance, autonomous coding agent, or backend service reads an existing database row, configuration object, or shared state record, modifies it in memory, and writes the updated state back to a storage layer accessible by concurrent processes, webhooks, or parallel agent turns. * **Does not apply when:** Inserting brand-new immutabl...",
    "decision_boundary": "1. **Are you reading a database record into memory, modifying an attribute or dictionary key, and saving it back?** Check whether another request or worker could touch that same record at the same time. If yes, either lock the row on read (`SELECT ... FOR UPDATE`) or gate the `UPDATE` on `WHERE id = ? AND version = ?`. 2. **Did you write `UPDATE ... WHERE id...",
    "operational_effect": "1. **Elimination of Blind Read-Modify-Write Overwrites:** Whenever generating code that reads, mutates, and writes back shared records, the instance enforces either optimistic Compare-And-Swap (`version` / `ETag` precondition + `rowcount` check) or pessimistic row locking (`SELECT ... FOR UPDATE`). 2. **Server-Side Atomic Increments for Counters:** For numer..."
  },
  "matched_failure_symptoms": [
    "LOST_UPDATE_OR_RACE_CONDITION"
  ],
  "composition_edges": {
    "primary_domain": "concurrency_locking_and_shared_resources",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/beneath-what-concurrency-and-backpressure-ceilings-must-an-instance-throttle-fan-out-tasks-to-prevent-file-descriptor-and-connection-pool-starvation.md",
      "https://corpusfetch.com/c/across-what-mandatory-tenant-predicate-scoping-and-row-level-security-gates-must-an-instance-isolate-multi-tenant-data-to-prevent-cross-tenant-data-leaks.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/across-what-readiness-unregistration-and-in-flight-drain-gates-must-an-instance-sequence-sigterm-shutdown-to-prevent-dropped-requests-and-truncated-writes.md",
      "https://corpusfetch.com/c/before-what-pre-flight-and-dry-run-gates-must-an-instance-stage-bulk-or-irreversible-mutations-to-prevent-unrecoverable-blast-radius-cascade.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/across-what-bounded-queue-admission-control-and-load-shedding-gates-must-an-instance-manage-concurrency-to-prevent-unbounded-memory-growth-and-tail-latency-collapse.md",
      "https://corpusfetch.com/c/across-what-concurrent-pipe-drain-and-ring-buffer-boundaries-must-an-instance-consume-subprocess-stdout-and-stderr-to-prevent-os-pipe-deadlocks-and-unbounded-output-oom.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "4a9e6ca721624b264cfbc29da1dce2cc33dc01640ec3ee1adff582580180772f",
    "verified_classes": [
      "OptimisticConcurrencyConflictError",
      "VersionedRecord",
      "CompareAndSwapVersionGate"
    ],
    "verified_functions": [
      "__init__",
      "create_initial",
      "read_snapshot",
      "compare_and_swap"
    ],
    "verified_functions_count": 4,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "KeyError",
      "OptimisticConcurrencyConflictError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}