{ "policy": { "version": 5, "patterns": { "version": 1, "method": "CURATED_PRACTICE_TOPIC", "notice": "Pattern topics identify design choices to practice. Read the ticket's acceptance criteria and justify the simplest suitable approach. Tags are not capability or ownership evidence; an untagged ticket has no curated pattern topic assigned." }, "fieldMix": { "version": 1, "method": "CURATED_ESTIMATE", "notice": "Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence." }, "contentStatus": "PRACTICE_BRIEF", "assessmentStatus": "NOT_QUALIFIED", "evidenceUse": "NONE", "aiPolicy": "AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior.", "notice": "Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included.", "outcomeEvidence": "Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.", "ownershipEvidence": "Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence." }, "patternTopics": [ { "id": "factory-method", "label": "Factory Method", "group": "Creational" }, { "id": "abstract-factory", "label": "Abstract Factory", "group": "Creational" }, { "id": "builder", "label": "Builder", "group": "Creational" }, { "id": "prototype", "label": "Prototype", "group": "Creational" }, { "id": "singleton", "label": "Singleton", "group": "Creational" }, { "id": "adapter", "label": "Adapter", "group": "Structural" }, { "id": "bridge", "label": "Bridge", "group": "Structural" }, { "id": "composite", "label": "Composite", "group": "Structural" }, { "id": "decorator", "label": "Decorator", "group": "Structural" }, { "id": "facade", "label": "Facade", "group": "Structural" }, { "id": "flyweight", "label": "Flyweight", "group": "Structural" }, { "id": "proxy", "label": "Proxy", "group": "Structural" }, { "id": "chain-of-responsibility", "label": "Chain of Responsibility", "group": "Behavioral" }, { "id": "command", "label": "Command", "group": "Behavioral" }, { "id": "interpreter", "label": "Interpreter", "group": "Behavioral" }, { "id": "iterator", "label": "Iterator", "group": "Behavioral" }, { "id": "mediator", "label": "Mediator", "group": "Behavioral" }, { "id": "memento", "label": "Memento", "group": "Behavioral" }, { "id": "observer", "label": "Observer", "group": "Behavioral" }, { "id": "state", "label": "State", "group": "Behavioral" }, { "id": "strategy", "label": "Strategy", "group": "Behavioral" }, { "id": "template-method", "label": "Template Method", "group": "Behavioral" }, { "id": "visitor", "label": "Visitor", "group": "Behavioral" }, { "id": "ports-and-adapters", "label": "Ports and Adapters", "group": "Architectural" }, { "id": "cqrs", "label": "CQRS", "group": "Architectural" }, { "id": "strangler-fig", "label": "Strangler Fig", "group": "Architectural" }, { "id": "saga", "label": "Saga", "group": "Distributed and reliability" }, { "id": "transactional-outbox", "label": "Transactional Outbox", "group": "Distributed and reliability" }, { "id": "circuit-breaker", "label": "Circuit Breaker", "group": "Distributed and reliability" }, { "id": "bulkhead", "label": "Bulkhead", "group": "Distributed and reliability" } ], "projects": [ { "id": "c502b2f2-cff3-432b-858c-1daa41526fe9", "key": "ACDC", "title": "Move customer preferences through a durable change feed", "field": "Data engineering", "summary": "Replicate a bounded preference dataset while preserving deletion and ordering semantics.", "context": "A fictional messaging service builds a read model from database changes. Restarts and schema changes can re-enable preferences that customers disabled.", "stack": [ "PostgreSQL", "TypeScript", "Object storage" ], "prerequisites": [ "Create synthetic preference records and a replayable local change log.", "Use adapters or fixtures without provisioning a production broker." ], "developerValue": "Practice change-feed ordering, snapshots and privacy-preserving deletion.", "companyValue": "Review whether replicated customer preferences remain correct during recovery.", "delivery": "Ten scoped tickets across three phases. Build a synthetic local service or select a ticket after recreating its prerequisites; estimates exclude setup.", "phases": [ { "id": "feed", "title": "Specify the change contract", "goal": "Identify ordering, identities and deletions." }, { "id": "replica", "title": "Build the projection", "goal": "Handle duplicates, schema changes and snapshot handoff." }, { "id": "repair", "title": "Repair feed gaps", "goal": "Detect divergence and recover scoped replicas." } ], "tickets": [ { "id": "81e372c8-d8fc-49f7-ba62-0d0e4fe4332e", "key": "ACDC-101", "title": "Define the preference change envelope with source position", "type": "TASK", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "feed", "dependsOn": [], "scenario": "The consumer sees a timestamp and payload but cannot distinguish two changes committed in the same millisecond.", "acceptanceCriteria": [ "Include stable source position, record identity and operation.", "Separate source commit time from consumer receipt time.", "Validate the envelope version before applying changes." ], "implementationNotes": [ "Use fabricated positions from a deterministic local log." ], "verification": [ "Parse two same-time changes with distinct positions.", "Reject an unknown envelope version without moving the checkpoint." ], "deliverables": [ "Change envelope schema" ], "rollout": "Publish the contract before consumer rollout; quarantine unsupported versions.", "skills": [ "Data contracts", "Ordering" ], "fieldMix": [ { "field": "Data engineering", "percentage": 60 }, { "field": "API design", "percentage": 20 }, { "field": "Distributed systems", "percentage": 20 } ], "patterns": [] }, { "id": "51c976e2-0df0-4285-87a0-e8df9dfa3106", "key": "ACDC-102", "title": "Redact preference change diagnostics without losing traceability", "type": "BUG", "priority": "HIGH", "difficulty": "FOUNDATIONAL", "estimateMinutes": 75, "phaseId": "feed", "dependsOn": [ "ACDC-101" ], "scenario": "Malformed preference payloads are dumped into generic logs with email addresses and free-text notes.", "acceptanceCriteria": [ "Log source position, safe record token and reason code.", "Exclude contact details and raw payload bodies.", "Retain restricted diagnostic access only through a scoped fixture store." ], "implementationNotes": [ "Use synthetic contact data in disclosure tests." ], "verification": [ "Locate a rejected envelope through its safe identifiers.", "Inject contact fields and assert they never appear in generic logs." ], "deliverables": [ "Sanitized diagnostics and disclosure checks" ], "rollout": "Deploy redaction before replay; restrict access to older diagnostic output.", "skills": [ "Privacy", "Observability" ], "fieldMix": [ { "field": "Privacy engineering", "percentage": 60 }, { "field": "Data engineering", "percentage": 40 } ], "patterns": [] }, { "id": "f0c28953-2ab2-4eca-9a51-45343b9863dc", "key": "ACDC-103", "title": "Represent preference deletion as a durable tombstone", "type": "STORY", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "feed", "dependsOn": [ "ACDC-101" ], "scenario": "A deleted record disappears from the source snapshot but remains enabled in a downstream projection indefinitely.", "acceptanceCriteria": [ "Define tombstones with identity and source position.", "Retain enough ordering metadata to reject stale recreation.", "Separate deletion from a false preference value." ], "implementationNotes": [ "Document retention assumptions for replayable tombstones." ], "verification": [ "Apply deletion and verify the projected record is absent.", "Replay an older enable event and keep the record deleted." ], "deliverables": [ "Tombstone contract and ordering cases" ], "rollout": "Enable tombstone production before cleanup; stop purging if replay coverage is uncertain.", "skills": [ "Deletion semantics", "Change data" ], "fieldMix": [ { "field": "Data engineering", "percentage": 70 }, { "field": "Database engineering", "percentage": 30 } ], "patterns": [] }, { "id": "ba4cda6b-197b-4e8f-9aa4-e4f658e3317c", "key": "ACDC-104", "title": "Advance the feed checkpoint only with the projected transaction", "type": "BUG", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 210, "phaseId": "replica", "dependsOn": [ "ACDC-101", "ACDC-103" ], "scenario": "The consumer acknowledges a change before updating the read model; a crash permanently loses the disabled preference.", "acceptanceCriteria": [ "Apply projection and checkpoint in one durable transaction.", "Duplicate delivery is a no-op at the same position.", "Failed application leaves the previous checkpoint intact." ], "implementationNotes": [ "Scope checkpoints to source partition and consumer generation." ], "verification": [ "Replay a committed change and keep one result.", "Fail between modeled projection and checkpoint writes and retry successfully." ], "deliverables": [ "Transactional consumer and interruption test" ], "rollout": "Canary one synthetic partition; stop consumption on checkpoint divergence.", "skills": [ "Transactions", "Idempotency" ], "fieldMix": [ { "field": "Database engineering", "percentage": 50 }, { "field": "Data engineering", "percentage": 50 } ], "patterns": [] }, { "id": "8f5ef06b-f68e-4104-91e2-1b39a5b070f6", "key": "ACDC-105", "title": "Reject a stale preference update after a partition retry", "type": "TASK", "priority": "MEDIUM", "difficulty": "ADVANCED", "estimateMinutes": 210, "phaseId": "replica", "dependsOn": [ "ACDC-104" ], "scenario": "A retry queue delivers an old enable event after a newer disable event has already committed.", "acceptanceCriteria": [ "Compare per-record source ordering before mutation.", "Retain stale-delivery counters without changing state.", "Treat equal position with different content as a conflict." ], "implementationNotes": [ "Do not use consumer wall time to resolve ordering." ], "verification": [ "Deliver disable before an older enable and retain disabled.", "Send contradictory equal-position data and quarantine the conflict." ], "deliverables": [ "Per-record ordering guard" ], "rollout": "Observe stale counts during canary; pause conflicting partitions instead of guessing order.", "skills": [ "Event ordering", "Conflict handling" ], "fieldMix": [ { "field": "Data engineering", "percentage": 60 }, { "field": "Distributed systems", "percentage": 40 } ], "patterns": [] }, { "id": "30271801-6be0-471d-8fa8-532e6216ddfb", "key": "ACDC-106", "title": "Handoff a preference snapshot to live changes without a gap", "type": "STORY", "priority": "MEDIUM", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "replica", "dependsOn": [ "ACDC-104", "ACDC-105" ], "scenario": "A new replica loads a snapshot while preferences continue changing, leaving a gap between export time and stream start.", "acceptanceCriteria": [ "Record an explicit snapshot boundary position.", "Buffer or replay changes after the boundary before activation.", "Keep the new generation unavailable until catch-up is complete." ], "implementationNotes": [ "Document source guarantees needed for a consistent boundary." ], "verification": [ "Change a preference during snapshot loading and reach final source state.", "Interrupt catch-up and verify readers still use the previous generation." ], "deliverables": [ "Snapshot handoff protocol and executable timeline" ], "rollout": "Build a shadow generation; restore the previous pointer if catch-up checks fail.", "skills": [ "Snapshot consistency", "Recovery" ], "fieldMix": [ { "field": "Data engineering", "percentage": 50 }, { "field": "Distributed systems", "percentage": 50 } ], "patterns": [] }, { "id": "42019ae5-ec7d-4c68-a4b5-94eeac29eb25", "key": "ACDC-107", "title": "Evolve a preference value enum without silently coercing unknown values", "type": "TASK", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "replica", "dependsOn": [ "ACDC-101", "ACDC-106" ], "scenario": "A new source value called paused is mapped to enabled by the old consumer's default branch.", "acceptanceCriteria": [ "Use an explicit compatibility map for each envelope version.", "Unknown values enter quarantine without checkpoint loss.", "Document how a compatible consumer resumes blocked input." ], "implementationNotes": [ "Avoid treating missing values as an affirmative preference." ], "verification": [ "Apply known values under both supported versions.", "Deliver paused to an incompatible consumer and verify no enable write." ], "deliverables": [ "Version compatibility matrix and consumer guard" ], "rollout": "Deploy compatible readers before writers; retain queued unsupported changes for replay.", "skills": [ "Schema evolution", "Fail-closed handling" ], "fieldMix": [ { "field": "Data engineering", "percentage": 70 }, { "field": "API design", "percentage": 30 } ], "patterns": [] }, { "id": "90e815c7-d1c8-4629-8802-a2c5acbbb460", "key": "ACDC-108", "title": "Compare source and replica preferences without exporting contacts", "type": "CHORE", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 180, "phaseId": "repair", "dependsOn": [ "ACDC-106", "ACDC-107" ], "scenario": "Operators suspect a gap but a full data export would spread contact information across incident tooling.", "acceptanceCriteria": [ "Compare keyed hashes and safe row counts by bounded scope.", "Report missing, extra and mismatched record tokens.", "Keep raw preference payloads out of the report." ], "implementationNotes": [ "Use stable canonical hashing and documented null handling." ], "verification": [ "Compare equal synthetic source and replica states.", "Alter one value and delete one row; identify both discrepancy categories." ], "deliverables": [ "Scoped reconciliation report" ], "rollout": "Run read-only reconciliation first; expire generated diagnostic artifacts after review.", "skills": [ "Reconciliation", "Privacy" ], "fieldMix": [ { "field": "Data engineering", "percentage": 60 }, { "field": "Privacy engineering", "percentage": 40 } ], "patterns": [] }, { "id": "4bf42677-4979-442a-bc68-edf6bb5e2584", "key": "ACDC-109", "title": "Repair one preference partition while continuing unrelated reads", "type": "TASK", "priority": "MEDIUM", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "repair", "dependsOn": [ "ACDC-106", "ACDC-108" ], "scenario": "One replica partition is corrupted; rebuilding the entire preference service would unnecessarily interrupt all accounts.", "acceptanceCriteria": [ "Rebuild only the selected source scope into a new generation.", "Catch up from the recorded boundary before pointer swap.", "Prevent repaired and old generations from mixing in one scoped read." ], "implementationNotes": [ "Require a dry-run plan and explicit partition identity." ], "verification": [ "Repair a synthetic partition and preserve unrelated output hashes.", "Interrupt before swap and retain complete reads from the old generation." ], "deliverables": [ "Partition repair command and atomic-read probe" ], "rollout": "Canary repair on a synthetic scope; switch its pointer back if reconciliation fails.", "skills": [ "Scoped recovery", "Consistency" ], "fieldMix": [ { "field": "Data engineering", "percentage": 50 }, { "field": "Distributed systems", "percentage": 30 }, { "field": "Database engineering", "percentage": 20 } ], "patterns": [] }, { "id": "3132975b-e0dd-4d83-b9e1-fbf264c0ad6c", "key": "ACDC-110", "title": "Expose replica freshness with a trustworthy unknown state", "type": "STORY", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "repair", "dependsOn": [ "ACDC-108", "ACDC-109" ], "scenario": "The dashboard marks a replica healthy when its consumer is running even though no source checkpoint has been observed.", "acceptanceCriteria": [ "Show applied source position and receipt lag separately.", "Report unknown when no comparable source watermark exists.", "Define stale thresholds in the local operating contract." ], "implementationNotes": [ "Never infer source completeness from process liveness." ], "verification": [ "Advance source and replica positions and calculate the documented lag.", "Remove the source watermark and return unknown health." ], "deliverables": [ "Freshness endpoint and unknown-state cases" ], "rollout": "Add freshness as advisory status first; restore the prior view while preserving unknown semantics.", "skills": [ "Observability", "Data semantics" ], "fieldMix": [ { "field": "Data engineering", "percentage": 60 }, { "field": "Site reliability", "percentage": 40 } ], "patterns": [] } ] } ] }