{ "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": "3ec41d1b-c6a4-4952-bbe9-7e76f0467449", "key": "ALEASE", "title": "Coordinate scheduled maintenance with fenced leases", "field": "Distributed systems", "summary": "Elect one active scheduler while preventing expired owners from mutating shared state.", "context": "A fictional document service runs periodic retention planning on multiple application instances. Paused instances resume after lease expiry and can overlap newer schedulers.", "stack": [ "TypeScript", "PostgreSQL" ], "prerequisites": [ "Create a synthetic maintenance queue and two independent scheduler clients.", "Use fake time where possible and no destructive real retention actions." ], "developerValue": "Practice lease assumptions, fencing and stale-owner rejection.", "companyValue": "Review safe coordination that remains explainable under pauses and 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": "authority", "title": "Define scheduler authority", "goal": "Model lease identity, expiry and protected actions." }, { "id": "coordination", "title": "Guard competing owners", "goal": "Acquire, renew and execute with fencing." }, { "id": "failure", "title": "Exercise time and connection failures", "goal": "Reconcile ownership and recover interrupted runs." } ], "tickets": [ { "id": "137c560f-3b37-4f30-8426-546e3aa40870", "key": "ALEASE-101", "title": "Specify scheduler lease state with a separate authority epoch", "type": "TASK", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "authority", "dependsOn": [], "scenario": "The scheduler table stores only owner name and expiry, so an old owner can appear identical to a later process with the same name.", "acceptanceCriteria": [ "Include lease identity, holder instance, expiry and monotonic epoch.", "Define active and expired semantics at the exact boundary.", "Keep display names outside authority checks." ], "implementationNotes": [ "Use opaque process-instance identities." ], "verification": [ "Represent two successive owners with distinct epochs.", "Reuse a display name and verify it cannot impersonate the previous instance." ], "deliverables": [ "Lease schema and authority contract" ], "rollout": "Review the schema before scheduler writes; leave coordination disabled until epoch checks exist.", "skills": [ "Lease modeling", "Identity" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 100 } ], "patterns": [] }, { "id": "0c584b13-0bed-4295-8275-3a3727ee254b", "key": "ALEASE-102", "title": "Use one authoritative clock boundary for lease decisions", "type": "TASK", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "authority", "dependsOn": [ "ALEASE-101" ], "scenario": "Two instances disagree about lease expiry because their local clocks differ by several seconds.", "acceptanceCriteria": [ "Define the clock used for acquisition and expiry checks.", "Keep client clock readings out of authority decisions.", "Document pause and network-delay assumptions." ], "implementationNotes": [ "Prefer database time within the transaction for this local PostgreSQL exercise." ], "verification": [ "Skew client clocks and obtain the same database lease decision.", "Reach exact expiry and verify the documented eligibility boundary." ], "deliverables": [ "Clock-bound lease queries and skew test" ], "rollout": "Canary lease reads under controlled skew; stop acquisition if authoritative time is unavailable.", "skills": [ "Clock semantics", "Distributed assumptions" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 100 } ], "patterns": [] }, { "id": "4ad58e6e-5ca0-4354-b547-5799b106f722", "key": "ALEASE-103", "title": "Classify maintenance actions that require fencing before side effects", "type": "TASK", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "authority", "dependsOn": [ "ALEASE-101", "ALEASE-102" ], "scenario": "The design adds a lease but assumes every downstream operation automatically knows whether its caller is still leader.", "acceptanceCriteria": [ "List each protected mutation and its fencing check location.", "Separate read-only planning from state-changing execution.", "Mark unfenceable external effects as unresolved." ], "implementationNotes": [ "Use synthetic retention plans; delete no real objects." ], "verification": [ "Trace a plan-state update to its epoch guard.", "Identify an external adapter without epoch support and block its destructive action." ], "deliverables": [ "Fencing coverage matrix" ], "rollout": "Require coverage before enabling actions; keep unresolved provider operations read-only.", "skills": [ "Boundary analysis", "Fencing" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 60 }, { "field": "System design", "percentage": 40 } ], "patterns": [] }, { "id": "1979cc45-8d18-4b81-a5b1-e35cf93ee238", "key": "ALEASE-104", "title": "Acquire a scheduler lease atomically under competing instances", "type": "STORY", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 210, "phaseId": "coordination", "dependsOn": [ "ALEASE-102", "ALEASE-103" ], "scenario": "Two instances see an expired lease and both believe they became the active scheduler.", "acceptanceCriteria": [ "Acquire through one guarded database transaction.", "Increment the epoch only for the winning acquisition.", "Return current safe ownership metadata to the loser." ], "implementationNotes": [ "Use two independent database connections and a barrier." ], "verification": [ "Race two acquisitions and assert one winning epoch.", "Hold a valid lease and verify another instance cannot replace it early." ], "deliverables": [ "Atomic acquisition command and race test" ], "rollout": "Canary with two local clients; stop scheduling if ownership results conflict.", "skills": [ "Transactions", "Leader coordination" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 60 }, { "field": "Database engineering", "percentage": 40 } ], "patterns": [] }, { "id": "40de2d15-5509-4231-b50e-871b4d3f67be", "key": "ALEASE-105", "title": "Renew a scheduler lease only for the current holder and epoch", "type": "BUG", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "coordination", "dependsOn": [ "ALEASE-104" ], "scenario": "A delayed renewal from an earlier process extends the newest owner's lease row while reporting success to the stale process.", "acceptanceCriteria": [ "Match holder instance and epoch in the renewal update.", "Bound extension duration from the authoritative clock.", "Return lost authority when no matching active lease exists." ], "implementationNotes": [ "Never renew solely by a shared scheduler name." ], "verification": [ "Renew the current owner successfully.", "Acquire a newer epoch, then submit the old renewal and reject it." ], "deliverables": [ "Guarded renewal and stale-message test" ], "rollout": "Enable guarded renewal before automated scheduling; make authority loss stop further work claims.", "skills": [ "Guarded updates", "Lease renewal" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 70 }, { "field": "Database engineering", "percentage": 30 } ], "patterns": [] }, { "id": "58209b0c-92e2-4cee-b9bb-9cfb19f4e7a6", "key": "ALEASE-106", "title": "Fence maintenance writes after a paused scheduler resumes", "type": "TASK", "priority": "HIGH", "difficulty": "EXPERT", "estimateMinutes": 300, "phaseId": "coordination", "dependsOn": [ "ALEASE-103", "ALEASE-104", "ALEASE-105" ], "scenario": "A scheduler pauses past expiry, then resumes a previously prepared plan after another instance has taken over.", "acceptanceCriteria": [ "Every protected write checks current authority epoch.", "A stale owner cannot complete or activate a plan.", "Record rejected stale activity without overwriting current progress." ], "implementationNotes": [ "Carry epoch through the command and recheck at commit." ], "verification": [ "Pause owner A, let B acquire, then finish B's plan.", "Resume A and verify its write is rejected even if it began earlier." ], "deliverables": [ "Commit-time fencing and pause reproduction" ], "rollout": "Canary synthetic plan activation; disable unfenced writes until every path passes the stale-owner probe.", "skills": [ "Fencing", "Concurrency" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 70 }, { "field": "Database engineering", "percentage": 30 } ], "patterns": [] }, { "id": "42696a4d-e7ab-4989-96d5-836fc981be39", "key": "ALEASE-107", "title": "Make scheduled maintenance occurrences idempotent across leadership changes", "type": "STORY", "priority": "MEDIUM", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "coordination", "dependsOn": [ "ALEASE-104", "ALEASE-106" ], "scenario": "A new leader repeats the current maintenance period and creates a second plan for the same logical occurrence.", "acceptanceCriteria": [ "Derive occurrence identity from schedule and intended UTC instant.", "Enforce one durable logical run per occurrence.", "Allow a new owner to resume existing nonterminal work safely." ], "implementationNotes": [ "Do not derive identity from acquisition time or process name." ], "verification": [ "Change leader midway through an occurrence and retain one run.", "Retry a terminal occurrence and return its recorded result." ], "deliverables": [ "Occurrence identity contract and leader-change test" ], "rollout": "Enable idempotent creation before multi-instance operation; reconcile existing duplicates through read-only reports.", "skills": [ "Idempotency", "Scheduling" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 60 }, { "field": "Database engineering", "percentage": 40 } ], "patterns": [] }, { "id": "3db026fe-17be-43ce-b013-09293946383b", "key": "ALEASE-108", "title": "Expose lease health without implying the holder is making progress", "type": "STORY", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "failure", "dependsOn": [ "ALEASE-105", "ALEASE-106", "ALEASE-107" ], "scenario": "A scheduler renews its lease while stuck on one task, so the status page incorrectly reports healthy processing.", "acceptanceCriteria": [ "Report lease authority and work-progress timestamps separately.", "Distinguish no leader, active leader and stalled work.", "Keep unknown progress explicit after observation gaps." ], "implementationNotes": [ "Use safe instance tokens rather than host secrets." ], "verification": [ "Show an active progressing scheduler.", "Freeze progress while renewing the lease and show stalled work." ], "deliverables": [ "Scheduler status projection" ], "rollout": "Add status before alert thresholds; disable noisy alerts while retaining raw safe state.", "skills": [ "Observability", "Health semantics" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 50 }, { "field": "Site reliability", "percentage": 50 } ], "patterns": [] }, { "id": "25e5fff8-6453-4db5-8197-414afa1d2b75", "key": "ALEASE-109", "title": "Recover coordination after a database connection partition", "type": "TASK", "priority": "MEDIUM", "difficulty": "EXPERT", "estimateMinutes": 300, "phaseId": "failure", "dependsOn": [ "ALEASE-102", "ALEASE-106", "ALEASE-108" ], "scenario": "An instance loses database connectivity but can still contact the fake work provider, raising the risk of acting on expired authority.", "acceptanceCriteria": [ "Stop new protected actions when authority cannot be verified.", "Reconcile lease and run state after reconnection.", "Resume only under a current valid epoch." ], "implementationNotes": [ "Use controlled local adapter disconnection, not real network disruption." ], "verification": [ "Disconnect one owner, acquire with another, and continue valid work.", "Reconnect the old owner and reject its cached authority before any action." ], "deliverables": [ "Partition drill and authority recovery trace" ], "rollout": "Run before multi-instance scheduling; fail closed on unresolved ownership.", "skills": [ "Network partitions", "Recovery" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 60 }, { "field": "Networking", "percentage": 20 }, { "field": "Site reliability", "percentage": 20 } ], "patterns": [] }, { "id": "80c76564-4352-4b87-b27e-9820f241ff7e", "key": "ALEASE-110", "title": "Document lease guarantees and the provider conditions they depend on", "type": "CHORE", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "failure", "dependsOn": [ "ALEASE-103", "ALEASE-107", "ALEASE-109" ], "scenario": "A release note says exactly one scheduler runs, even though stale processes may execute until downstream fences reject their writes.", "acceptanceCriteria": [ "Describe mutual authority separately from process execution.", "List clock, transaction and provider fencing assumptions.", "Link each guarantee to a race or partition probe." ], "implementationNotes": [ "Avoid claiming leases alone guarantee exactly-once effects." ], "verification": [ "Trace a protected-write guarantee to its fencing test.", "Identify an unfenced provider and state the unsupported guarantee." ], "deliverables": [ "Coordination operating contract" ], "rollout": "Review before enabling external actions; revise the contract when provider semantics change.", "skills": [ "Distributed reasoning", "Technical communication" ], "fieldMix": [ { "field": "Distributed systems", "percentage": 60 }, { "field": "System design", "percentage": 40 } ], "patterns": [] } ] } ] }