# noCV engineering task library Content version 5 Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs. Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence. ## CTIER — A local archive cache with explicit integrity and capacity Fictional media archive Ash serves generated byte fixtures through a fast local cache and slower provider stub. Both tiers run locally. **Field:** Storage systems. **Suggested stack:** TypeScript, Filesystem adapter, Vitest. **Engineer value:** Practice cache correctness, request coalescing and capacity control. **Company value:** Inspect whether faster delivery preserves bytes and operating limits. **Delivery agreement:** Use dedicated fixture directories and publish measured local observations only. ### Setup prerequisites - Create immutable generated blobs with known digests. - Implement controllable cache and origin adapters with read failures. ### Define cache reads Keep source authority explicit. #### CTIER-101 — Keep archive cache misses distinct from provider failures **Bug · Medium priority · Foundational** noCV practice brief v5 · CTIER-101 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Define cache reads. Depends on: No preceding ticket. Difficulty: Foundational. Estimated focused work: 60 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 70% · Site reliability 30%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Any cache read error is treated as a miss and hides damaged storage. Define typed outcomes. Acceptance criteria - Missing key is a miss - Permission failure is operational error - Origin reads follow documented fallback policy Implementation constraints - Do not swallow arbitrary filesystem exceptions. Verification - Read absent fixture - Inject permission failure Deliverables - Cache result contract Rollout and recovery: Bypass cache on operational failure while reporting it. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-102 — Key archive cache entries by immutable blob identity **Task · Medium priority · Foundational** noCV practice brief v5 · CTIER-102 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Define cache reads. Depends on: CTIER-101. Difficulty: Foundational. Estimated focused work: 75 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 70% · Performance engineering 30%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. A mutable filename reuses stale cached bytes after replacement. Bind entries to immutable version or digest. Acceptance criteria - Same identity reuses entry - New version uses new key - User labels do not affect identity Implementation constraints - Tenant scope remains part of lookup authority. Verification - Read repeated identity - Replace logical filename with new version Deliverables - Cache-key contract and cases Rollout and recovery: Disable cache reuse if identity is uncertain. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-103 — Verify archive cache fills before promoting temporary bytes **Task · High priority · Intermediate** noCV practice brief v5 · CTIER-103 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Define cache reads. Depends on: CTIER-102. Difficulty: Intermediate. Estimated focused work: 135 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 100%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Interrupted origin reads leave files that future requests treat as complete. Stage and verify each fill. Acceptance criteria - Fill checks declared digest - Unverified files stay invisible - Failed fill removes or quarantines its temporary file Implementation constraints - Promotion must not expose partial bytes. Verification - Fill valid fixture - Truncate origin stream Deliverables - Verified fill and failure cases Rollout and recovery: Disable cache writes while serving origin directly. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. ### Control cache mutation Handle contention and eviction. #### CTIER-104 — Coalesce concurrent archive cache fills for one blob **Bug · Medium priority · Advanced** noCV practice brief v5 · CTIER-104 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Control cache mutation. Depends on: CTIER-103. Difficulty: Advanced. Estimated focused work: 165 minutes; setup and prerequisite tickets are additional. Estimated field mix: Performance engineering 50% · Storage systems 50%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Ten simultaneous misses download the same object ten times. Share one fill without joining unrelated keys. Acceptance criteria - Same identity shares fill - Different identities remain independent - Failure releases waiters consistently Implementation constraints - Bound the in-flight map and clear settled entries. Verification - Issue concurrent same-key reads - Fail shared fill then retry Deliverables - Fill coordinator and concurrency cases Rollout and recovery: Disable coalescing if waiters cannot be released. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-105 — Enforce archive cache capacity before admitting a fill **Task · High priority · Advanced** noCV practice brief v5 · CTIER-105 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Control cache mutation. Depends on: CTIER-103, CTIER-104. Difficulty: Advanced. Estimated focused work: 180 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 50% · Performance engineering 50%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Parallel fills exceed the configured cache budget because each sees free space. Reserve capacity atomically. Acceptance criteria - Active reservations count toward limit - Failed fills release reservation - Oversized objects bypass with explanation Implementation constraints - Include temporary bytes in capacity accounting. Verification - Admit fitting concurrent fills - Attempt object larger than budget Deliverables - Admission reservations and cases Rollout and recovery: Stop cache admission until accounting reconciles. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-106 — Avoid evicting archive blobs while active readers hold them **Bug · High priority · Expert** noCV practice brief v5 · CTIER-106 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Control cache mutation. Depends on: CTIER-105. Difficulty: Expert. Estimated focused work: 240 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 80% · Backend 20%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Eviction deletes a file while a streaming reader still needs it. Define reader leases and reclamation behavior. Acceptance criteria - Active readers finish or fail explicitly by contract - New reads cannot acquire deleting entry - Released leases permit eviction Implementation constraints - Specify platform filesystem assumptions. Verification - Evict idle fixture - Race eviction with active reader Deliverables - Reader-lease protocol and race tests Rollout and recovery: Pause eviction if active-reader safety is uncertain. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-107 — Record archive cache recency without writing on every byte read **Chore · Medium priority · Intermediate** noCV practice brief v5 · CTIER-107 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Control cache mutation. Depends on: CTIER-104, CTIER-106. Difficulty: Intermediate. Estimated focused work: 120 minutes; setup and prerequisite tickets are additional. Estimated field mix: Performance engineering 60% · Storage systems 40%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Streaming a large blob rewrites recency metadata for every chunk. Update recency at a bounded operation boundary. Acceptance criteria - One read causes bounded metadata writes - Eviction order remains documented - Failed read policy is explicit Implementation constraints - Use injected clocks for recency tests. Verification - Stream many chunks - Fail midway and inspect recency Deliverables - Recency policy and write-count checks Rollout and recovery: Use insertion order temporarily if recency updates regress. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. ### Repair and observe Recover damage without hiding uncertainty. #### CTIER-108 — Detect corrupted archive cache entries before serving them again **Task · High priority · Advanced** noCV practice brief v5 · CTIER-108 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Repair and observe. Depends on: CTIER-103, CTIER-106. Difficulty: Advanced. Estimated focused work: 180 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 80% · Site reliability 20%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. A local byte flip persists across reads. Add a bounded verification policy and quarantine path. Acceptance criteria - Verification detects mismatch - Corrupt entry is not reused - Origin repair creates a new verified entry Implementation constraints - State whether verification occurs per read or scheduled scan. Verification - Corrupt fixture then read - Fail origin repair Deliverables - Integrity policy and repair cases Rollout and recovery: Bypass cache for quarantined identities. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-109 — Reconcile archive cache metadata after process restart **Bug · High priority · Advanced** noCV practice brief v5 · CTIER-109 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Repair and observe. Depends on: CTIER-105, CTIER-108. Difficulty: Advanced. Estimated focused work: 180 minutes; setup and prerequisite tickets are additional. Estimated field mix: Storage systems 80% · Site reliability 20%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. A restart leaves reservations and temporary files consuming phantom capacity. Rebuild accounting from valid state. Acceptance criteria - Abandoned reservations release - Verified entries remain counted - Unknown files are quarantined rather than silently trusted Implementation constraints - Cleanup only within the configured fixture root. Verification - Restart after successful fill - Crash with partial temporary file Deliverables - Startup reconciliation and cases Rollout and recovery: Start cache read-only until reconciliation completes. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence. #### CTIER-110 — Report archive cache hit rates with a defined denominator **Chore · Low priority · Intermediate** noCV practice brief v5 · CTIER-110 · A local archive cache with explicit integrity and capacity Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included. Phase: Repair and observe. Depends on: CTIER-107, CTIER-109. Difficulty: Intermediate. Estimated focused work: 105 minutes; setup and prerequisite tickets are additional. Estimated field mix: Site reliability 50% · Performance engineering 30% · Storage systems 20%. Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence. Dashboard hit rate counts every chunk and exaggerates cache usefulness. Count logical read outcomes explicitly. Acceptance criteria - Denominator is logical read attempts - Bypass and errors are separate - No blob content enters events Implementation constraints - Report local measurements without generalized performance claims. Verification - Read hit miss and bypass fixtures - Retry failed read and inspect counts Deliverables - Metrics contract and captured examples Rollout and recovery: Hide hit-rate panel if event accounting changes. Project prerequisites: Create immutable generated blobs with known digests. Implement controllable cache and origin adapters with read failures. Engineer value: Practice cache correctness, request coalescing and capacity control. Company value: Inspect whether faster delivery preserves bytes and operating limits. AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior. Planning status does not create Outcome Evidence or Ownership Evidence.