D-28: Dialogue — snapshot + unit tests (parser, reducer, views)

[kirich1409]

Description

Bring the Dialogue feature to adequate test coverage — parser fixtures, reducer TestStore cases, view snapshots across appearances.

Spec: Epic #250 §9 acceptance criteria.

Scope

Parser tests (AgentChatTests/Parser/)

Extend fixtures from D-8:

• 20+ real JSONL snippets covering every event type from spec §2.
• Dedup test with reconnect-like duplicate streams.
• Overflow (10+ MiB single line) drop + continue test.
• Tolerant decode (unknown fields in known type).
• Partial-line (byte-by-byte feeding).
• Unknown event type → .unknownEvent(raw:).

Reducer tests (AgentChatTests/Reducer/)

TestStore flows:

• Happy path: init → text response → tool_use → tool_result → completed → result.
• Tool failure path.
• API retry → recovered.
• Rate limit rejected → status .error.
• Compact boundary divider.
• Interrupt mid-stream.
• Unknown event logging.
• Cost threshold crossed → costAlertShown = true.

View snapshot tests (AgentChatUISnapshotTests/)

Using pointfreeco/swift-snapshot-testing:

• All 12 tool widgets × 4 appearances (light/dark/HCR/reduceTransparency) — populated / collapsed / expanded states.
• Message views — short / long / multi-segment × 4 appearances.
• ThinkingIndicator — collapsed / expanded / streaming / completed.
• DialogueView composite — empty / streaming / tool running / error / rate-limited.
• PreflightErrorView — each reason variant.
• StreamInspectorView — filtered / unfiltered.

Coverage target

Not aiming for % metric — aim for flow coverage. Every user-visible state of every view should have at least one snapshot; every reducer transition should have at least one TestStore case.

Acceptance Criteria

• Parser test suite passes with 20+ fixtures covering spec.
• Reducer TestStore suite passes with 8+ flows.
• Snapshot tests cover all widgets + views × 4 appearances.
• swift test in each new package passes.
• CI Swift step extended to run both packages' tests.
• Snapshot reference images committed.

Relationships

• Parent issue: EPIC: Dialogue — structured chat UI for agent sessions #250
• Blocked by: #D-8, #D-10, #D-13 through #D-19, #D-26
• Blocks: release (MVP acceptance)