SubMiner/backlog/tasks/task-27.4 - Split-mpv-service.ts-into-protocol-transport-property-and-facade-layers.md

id, title, status, assignee, created_date, updated_date, labels, dependencies, references, documentation, parent_task_id, priority

id	title	status	assignee	created_date	updated_date	labels	dependencies	references	documentation	parent_task_id	priority
TASK-27.4	Split mpv-service.ts into protocol, transport, property, and facade layers	To Do	backend	2026-02-13 17:13	2026-02-13 21:15	owner:backend	TASK-27.1	src/core/services/mpv-service.ts	docs/architecture.md	TASK-27	high

Description

Split mpv-service.ts (773 LOC) into thin, testable layers without changing wire protocol behavior.

This task absorbs the scope of TASK-8 (Reduce MpvIpcClient deps interface and separate protocol from application logic). The work proceeds in two phases:

Phase A (was TASK-8): Separate protocol from application logic

• Reduce the 22-property MpvIpcClientDeps interface to protocol-level concerns only
• Move application-level reactions (subtitle broadcast, overlay visibility sync, timing tracking) to event emitter or external listener pattern
• Make MpvIpcClient testable without mocking 22 callbacks

Phase B: Physical file split

• Create submodules for: protocol parsing/dispatch, connection lifecycle/retry, property subscriptions/state mapping
• Wire the public facade to maintain API compatibility for all existing consumers

Acceptance Criteria

• #1 MpvIpcClient deps interface reduced to protocol-level concerns only (from current 22 properties).
• #2 Application-level reactions (subtitle broadcast, overlay sync, timing) handled via event emitter or external listeners registered by main.ts.
• #3 Create submodules for protocol parsing/dispatch, connection lifecycle/retry, and property subscriptions/state mapping.
• #4 The public mpv service API (MpvClient interface) remains compatible for all existing consumers.
• #5 MpvIpcClient is testable without mocking 22 callbacks — protocol layer tests need only socket-level mocks.
• #6 Add at least one focused regression check for reconnect + property update flow.
• #7 Document expected event flow in docs/structure-roadmap.md.

Implementation Notes

TASK-8 Absorption

TASK-8 and TASK-27.4 overlapped significantly:

• TASK-8: "Separate protocol from application logic" + shrink deps interface
• TASK-27.4: "Split into protocol, transport, property, and facade layers"

TASK-27.4 is TASK-8 + physical file splitting. Running them as separate tasks would mean touching the same file twice with the same goals. Now consolidated as Phase A (interface separation) and Phase B (file split) within a single task.

TASK-8 should be marked as superseded once this task begins.

Dependency Note

Original plan listed TASK-8 as a dependency. Since TASK-8's scope is now absorbed here, the only remaining dependency is TASK-27.1 (inventory/contracts map).