CDOWN-104 · Handle transfer boundaries

Resume a mobile course transfer only with matching content identity

Practice briefStoryAdvanced

A paused transfer resumes after content changed and produces mixed bytes. Bind ranges to a manifest version.

Focused work estimate: 3h + prerequisites
Priority in the scenario: High
Engineering practice: HTTP · Integrity

Estimated field mix

Storage systems40%
Networking30%
Mobile30%

Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.

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Project context

Fictional learning app Birch offers synthetic text and small local media fixtures through a loopback adapter. No copyrighted course assets or network accounts are needed.

Setup prerequisites

Create small local byte fixtures and a range-response stub.
Simulate low storage, interruptions and stale manifests.

Preceding work

Complete these dependencies, or supply their agreed outputs before taking this ticket.

Acceptance criteria

Resume checks content identity
Mismatch discards incompatible partial bytes
Restart remains explicit in UI

Implementation constraints

Treat ETags as opaque validators.

Verification to include

Resume unchanged fixture
Change validator during pause

Deliverables

Range-resume coordinator

Rollout and recovery

Disable resume and restart from zero safely.

Value of the work

For the engineer: Practice mobile file lifecycles and background state recovery.

For the team: Inspect predictable resource usage and truthful download status.

Evidence boundaries

Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.

Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.