{
  "schema_version": "1.3.0",
  "slug": "across-what-migration-and-expand-contract-phases-must-an-instance-decouple-stateful-schema-mutations-from-application-deployments-to-prevent-zero-downtime-lockouts",
  "title": "Across what migration and expand-contract phases must an instance decouple stateful schema mutations from application deployments to prevent zero-downtime lockouts?",
  "date_of_record": "2026 October 20",
  "scope": "* **Applies when:** Modifying database schemas, stateful storage layouts, or serialized wire contracts in systems serving continuous live traffic or supporting rolling deployments and rollbacks. * **Does not apply when:** Initializing green",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/across-what-migration-and-expand-contract-phases-must-an-instance-decouple-stateful-schema-mutations-from-application-deployments-to-prevent-zero-downtime-lockouts.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/across-what-migration-and-expand-contract-phases-must-an-instance-decouple-stateful-schema-mutations-from-application-deployments-to-prevent-zero-downtime-lockouts.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/across-what-migration-and-expand-contract-phases-must-an-instance-decouple-stateful-schema-mutations-from-application-deployments-to-prevent-zero-downtime-lockouts.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 2174,
    "python_slice_tokens": 380,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "In production systems serving live traffic across rolling application deployments (`App_v1` and `App_v2` running simultaneously during rollout), database state is shared across both versions at once. A catastrophic outage occurs when an instance **couples a breaking schema mutation (such as `ALTER TABLE RENAME COLUMN`, `DROP COLUMN`, or adding a `NOT NULL` c...",
    "what_was_observed": "When autonomous instances generate database migrations and application code changes in a single coupled step, four primary production failure modes occur: 1. **Rolling-Deploy `N-1` Application Crash:** Migration `004_rename_email.sql` renames `user_email` to `primary_email` before `App_v2` finishes rolling out; the 50% of traffic still routed to `App_v1` pods crashes instantly with `column \"user_email\" does not exist...",
    "condition_of_validity": "* **Applies when:** Modifying database schemas, stateful storage layouts, or serialized wire contracts in systems serving continuous live traffic or supporting rolling deployments and rollbacks. * **Does not apply when:** Initializing greenfield tables in an empty development database with zero existing rows and zero concurrent readers. * **Non-binding outsi...",
    "decision_boundary": "1. **Will older application instances still running during your rollout crash if this migration runs right now?** If so, split the change into an additive Expand phase first and save the destructive Contract phase until every old instance is drained. 2. **What happens if your `ALTER TABLE` statement has to wait behind a slow query?** Always set a short `lock...",
    "operational_effect": "1. **Zero Rolling-Deploy `N-1` Crashes:** Schema changes remain strictly additive until all legacy application readers and writers have been decommissioned. 2. **Elimination of Lock-Queue Outages:** Mandatory `lock_timeout` guards and `CONCURRENTLY` / `NOT VALID` primitives prevent exclusive table lock convoys. 3. **Preserved Instant Rollback Safety:** Dual-..."
  },
  "matched_failure_symptoms": [
    "SCHEMA_DRIFT_OR_COERCION_CRASH"
  ],
  "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": "401718c4f35d6e1e4e438170f6e072288669974a6410b95d07ce700f6fb4a0ff",
    "verified_classes": [
      "UnsafeZeroDowntimeMigrationError",
      "MigrationPhase",
      "MigrationSafetyAudit",
      "ExpandContractMigrationGate"
    ],
    "verified_functions": [
      "audit_sql_migration"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "UnsafeZeroDowntimeMigrationError"
    ],
    "sample_fail_closed_invariants": [],
    "stdlib_dependencies": [
      "dataclasses",
      "enum",
      "re",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}