{ "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": [ { "key": "SIPC", "title": "Supervise local worker processes without losing their output", "field": "Systems programming", "summary": "Build framed IPC, bounded buffering, process lifecycle control and restart-safe request identity.", "context": "A fictional document converter launches local sandbox substitutes as child processes. Its prototype parses newline-delimited output, leaks descriptors, and retries requests after ambiguous worker exits. Create a Rust supervisor and deterministic worker fixtures; no document content or production sandbox is supplied.", "stack": [ "Rust", "Child processes", "Unix sockets or named pipes", "Vitest or cargo test" ], "prerequisites": [ "File descriptors", "Framing", "Process signals" ], "developerValue": "Practice IPC contracts, resource inheritance, process supervision and ambiguous completion.", "companyValue": "Review a local worker boundary that contains crashes and preserves request outcomes before connecting an isolated execution provider.", "delivery": "Ten linked tickets across three phases. Use synthetic inputs and a local harness; provide source, focused tests, measurements where requested, and a recovery note.", "phases": [ { "id": "model", "title": "Establish the machine contract", "goal": "Make representation, ownership and failure boundaries explicit." }, { "id": "control", "title": "Control resources and concurrency", "goal": "Implement bounded behavior under realistic interleavings." }, { "id": "operate", "title": "Prove recovery and handoff", "goal": "Measure, diagnose and safely replace the component." } ], "tickets": [ { "id": "36749fbb-c8fc-48cd-a96a-b504b7b7c0ed", "key": "SIPC-101", "title": "Frame worker messages without treating newlines as boundaries", "type": "TASK", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "model", "dependsOn": [], "scenario": "A diagnostic string contains a newline and splits one response into two apparent messages.", "acceptanceCriteria": [ "Frame declares version, type, request identity, and bounded payload length", "Reader handles partial headers and payloads", "Unknown versions fail without consuming the next frame" ], "implementationNotes": [ "Cap frame size before allocating its payload buffer." ], "verification": [ "Read several frames split across every header boundary.", "Advertise an oversized or truncated payload and verify bounded rejection." ], "deliverables": [ "Versioned frame codec and fragmentation tests" ], "rollout": "Keep the line protocol available only for old local fixtures during migration.", "skills": [ "Binary protocols", "Input validation" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "API design", "percentage": 30 } ], "patterns": [] }, { "id": "64ff2e43-105b-4cd5-9cd2-881d56087400", "key": "SIPC-102", "title": "Close inherited descriptors before executing the worker", "type": "BUG", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "model", "dependsOn": [], "scenario": "A child inherits the supervisor listener and keeps it open after the parent exits, preventing clean restart.", "acceptanceCriteria": [ "Child receives only declared stdin, stdout, stderr, and control handles", "Supervisor closes duplicate ends after spawn", "Restart can bind the same local endpoint" ], "implementationNotes": [ "Do not depend on a global close-all scan that races other threads opening handles." ], "verification": [ "Spawn, complete, and restart a worker while checking descriptor counts.", "Add an undeclared inheritable handle and confirm the fixture detects it." ], "deliverables": [ "Spawn handle policy and leak regression" ], "rollout": "Audit handle inheritance before enabling multiple workers.", "skills": [ "Process spawning", "Resource cleanup" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Security", "percentage": 30 } ], "patterns": [] }, { "id": "9c0d3081-a6bd-4512-a3cf-a68db6b9567f", "key": "SIPC-103", "title": "Correlate out-of-order worker replies to the right caller", "type": "STORY", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "model", "dependsOn": [ "SIPC-101" ], "scenario": "Two conversions finish in reverse order and the supervisor resolves the first waiter with the second result.", "acceptanceCriteria": [ "Every accepted request has a unique operation identity", "Replies resolve only the matching pending request", "Duplicate and unknown replies are recorded without completing another caller" ], "implementationNotes": [ "Keep the pending map bounded by admission capacity and deadlines." ], "verification": [ "Complete three requests in reverse order and verify each result.", "Send a duplicate and an unknown identity and confirm pending callers remain unchanged." ], "deliverables": [ "Correlation table and ordering tests" ], "rollout": "Enable concurrent requests only after correlation checks pass.", "skills": [ "Correlation IDs", "Concurrency" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Distributed systems", "percentage": 30 } ], "patterns": [] }, { "id": "4fb92f59-13b2-463f-ba7f-7a5feb290b0d", "key": "SIPC-104", "title": "Separate protocol output from worker diagnostics", "type": "CHORE", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "control", "dependsOn": [ "SIPC-101", "SIPC-102" ], "scenario": "A library warning written to stdout is parsed as a reply and closes the worker connection.", "acceptanceCriteria": [ "Protocol frames use one declared channel", "Diagnostics use stderr with bounded capture", "Malformed protocol bytes fail the request without hiding diagnostics" ], "implementationNotes": [ "Sanitize diagnostics and cap retained bytes per worker." ], "verification": [ "Return a valid response while writing warnings to stderr.", "Write nonprotocol bytes on the protocol channel and verify isolated failure." ], "deliverables": [ "Channel contract and mixed-output fixtures" ], "rollout": "Treat unexpected stdout as a worker defect during local migration.", "skills": [ "Process I/O", "Diagnostics" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Developer tooling", "percentage": 30 } ], "patterns": [] }, { "id": "22ae357c-b779-4cb2-af5d-b885dc64e6b6", "key": "SIPC-105", "title": "Apply backpressure when a worker stops reading", "type": "TASK", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "control", "dependsOn": [ "SIPC-103", "SIPC-104" ], "scenario": "A stalled child leaves the supervisor buffering every request body until memory is exhausted.", "acceptanceCriteria": [ "Per-worker and global pending byte limits are enforced", "Admission reports overload before consuming the body", "Healthy workers can continue within their own capacity" ], "implementationNotes": [ "Do not solve the stall with an unbounded retry queue." ], "verification": [ "Drive balanced workers to their declared capacity.", "Pause one reader and prove buffers remain bounded while another worker progresses." ], "deliverables": [ "IPC admission controller and stalled-reader test" ], "rollout": "Start with small limits and expose overload to callers.", "skills": [ "Backpressure", "Resource isolation" ], "fieldMix": [ { "field": "Systems programming", "percentage": 60 }, { "field": "Performance engineering", "percentage": 40 } ], "patterns": [ { "pattern": "bulkhead", "activity": "APPLY", "focus": "Isolate each child process buffer and preserve global capacity so one stopped reader cannot consume every supervisor resource." } ] }, { "id": "6995a556-fce5-42e4-b007-06bed5fd4f4a", "key": "SIPC-106", "title": "Classify worker exit before deciding whether to retry", "type": "BUG", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "control", "dependsOn": [ "SIPC-103" ], "scenario": "The worker exits after writing its output but before the acknowledgement frame; automatic retry may produce a second external artifact.", "acceptanceCriteria": [ "Outcome distinguishes not-started, running, acknowledged, failed, and unknown", "Unknown completion requires status lookup or explicit review", "Retry reuses the stable operation identity" ], "implementationNotes": [ "Do not infer failure solely from pipe closure or process exit code." ], "verification": [ "Exercise exits before start and after acknowledged completion.", "Exit after effect but before acknowledgement and preserve UNKNOWN without blind retry." ], "deliverables": [ "Exit classification state machine and ambiguity fixtures" ], "rollout": "Disable automatic retry for unknown outcomes until the worker supports reconciliation.", "skills": [ "Distributed failure", "Idempotency", "State machines" ], "fieldMix": [ { "field": "Systems programming", "percentage": 60 }, { "field": "Distributed systems", "percentage": 40 } ], "patterns": [] }, { "id": "99f143fa-585f-47c0-af09-c74cc2255eb8", "key": "SIPC-107", "title": "Terminate a process tree without signaling unrelated work", "type": "STORY", "priority": "HIGH", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "control", "dependsOn": [ "SIPC-102", "SIPC-106" ], "scenario": "A timed-out worker launches a helper. Killing only the parent leaks the helper; reusing a process-group identifier risks signaling a newer process.", "acceptanceCriteria": [ "Each operation owns a fresh supervised process group or platform job object", "Termination verifies the group identity before signaling", "Cleanup observes all declared descendants or reports unresolved members" ], "implementationNotes": [ "Tests use inert local helpers and never enumerate or signal arbitrary host processes." ], "verification": [ "Terminate a fixture parent and its two waiting children.", "Reuse a synthetic numeric identifier and prove identity validation blocks the stale cleanup." ], "deliverables": [ "Process-tree lifecycle adapter and safe termination tests" ], "rollout": "Keep worker concurrency at one until descendant cleanup is reliable.", "skills": [ "Process groups", "Identity fencing", "Cleanup" ], "fieldMix": [ { "field": "Systems programming", "percentage": 60 }, { "field": "Security", "percentage": 40 } ], "patterns": [] }, { "id": "c7702989-e5a3-4afa-b275-bf5af95f87a9", "key": "SIPC-108", "title": "Restart crashed workers without retry storms", "type": "CHORE", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "operate", "dependsOn": [ "SIPC-105", "SIPC-106" ], "scenario": "A corrupt fixture crashes every replacement worker, and immediate restart loops consume the supervisor CPU.", "acceptanceCriteria": [ "Restart budget uses bounded attempts and backoff", "Stable runtime resets the failure window", "Exhaustion opens a visible unavailable state" ], "implementationNotes": [ "Use injected time and deterministic jitter; do not sleep in tests." ], "verification": [ "Crash twice, recover, and verify the budget clears after stability.", "Crash every replacement and confirm restart attempts stop at the bound." ], "deliverables": [ "Restart policy and crash-loop test" ], "rollout": "Fail new requests fast while a worker class is unavailable.", "skills": [ "Supervision", "Backoff", "Failure isolation" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Site reliability", "percentage": 30 } ], "patterns": [ { "pattern": "circuit-breaker", "activity": "APPLY", "focus": "Open a bounded unavailable state after repeated worker crashes so replacement attempts stop until the declared recovery probe." } ] }, { "id": "2b2c45a8-78da-429f-b580-cbe94eac9a12", "key": "SIPC-109", "title": "Reconcile pending operations after supervisor restart", "type": "TASK", "priority": "HIGH", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "operate", "dependsOn": [ "SIPC-103", "SIPC-106", "SIPC-108" ], "scenario": "The supervisor restarts with requests marked running but no in-memory correlation table and no proof whether workers completed them.", "acceptanceCriteria": [ "Persist stable operation identity and last acknowledged state before dispatch", "Recovery queries a deterministic worker ledger when supported", "Unresolved operations remain visible and are never silently marked failed" ], "implementationNotes": [ "The local ledger contains synthetic identities and bounded metadata, not document bodies." ], "verification": [ "Restart after acknowledgement and restore the completed result.", "Restart during an unqueryable effect and retain UNKNOWN for review." ], "deliverables": [ "Pending-operation journal and restart drill" ], "rollout": "Require reconciliation support before enabling autonomous retry.", "skills": [ "Crash recovery", "Journaling", "Idempotency" ], "fieldMix": [ { "field": "Systems programming", "percentage": 60 }, { "field": "Storage systems", "percentage": 40 } ], "patterns": [] }, { "id": "2a7e116d-a6c6-4d14-913d-61b6b8ea8dad", "key": "SIPC-110", "title": "Document the IPC boundary for a future isolated provider", "type": "BUG", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "operate", "dependsOn": [ "SIPC-107", "SIPC-108", "SIPC-109" ], "scenario": "The local child-process harness is about to be mistaken for a production candidate-code sandbox.", "acceptanceCriteria": [ "Document framing, resource limits, process identity, shutdown, and unresolved outcomes", "State which isolation guarantees the local supervisor does not provide", "Define the provider contract a hardened external executor must satisfy" ], "implementationNotes": [ "Do not claim namespace, secret, network, or host isolation from ordinary child processes." ], "verification": [ "Reproduce the local crash and restart drill from the guide.", "Attempt to select the local adapter under a production configuration and require fail-closed behavior." ], "deliverables": [ "IPC contract and explicit production boundary note" ], "rollout": "Keep the local supervisor restricted to synthetic development fixtures.", "skills": [ "Provider interfaces", "Security boundaries", "Documentation" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Platform engineering", "percentage": 30 } ], "patterns": [] } ], "id": "a40a56f5-00da-4afb-b1fb-38fe8499c4be" } ] }