Emit structuredContent on 7 MCP tool handlers#117
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obj-p merged 1 commit intocli-mcp-parityfrom Apr 16, 2026
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The MCP Swift SDK exposes CallTool.Result.structuredContent: Value?
alongside the traditional [Tool.Content] blocks. Populate it on every
tool handler that returns non-trivial data so clients (CLI scripts
via --json, MCP agents via structured consumption) can consume a
typed payload instead of regex-parsing prose.
Shared DTOs live in Sources/PreviewsCLI/DaemonProtocol.swift — a
caseless-enum namespace with nested Codable structs. Kept separate
from domain types (e.g. PreviewInfoDTO vs PreviewsCore.PreviewInfo)
so the wire contract can drift independently.
Migrated handlers:
- preview_start → PreviewStartResult { sessionID, platform,
sourceFilePath, deviceUDID?, pid?, traits?, previews[], activeIndex,
setupWarning? }
- preview_variants → VariantsResult { variants[], successCount,
failCount }. Each variant carries status="ok"|"error" plus
imageIndex pointing into the sibling content array (for success) or
an error string (for failure).
- preview_switch → SwitchResult { sessionID, activeIndex, traits?,
previews[] }. previews[].active replaces the " <- active" marker.
- preview_list → PreviewListResult { file, previews[] }.
- simulator_list → SimulatorListResult { simulators[] }.
- session_list → SessionListResult { sessions[] }. The tab-delimited
text body is now rendered from the DTO list.
- preview_elements → { sessionID, elements: <tree> } as a raw Value.
The accessibility tree is opaque WDA JSON, round-tripped natively
rather than mirrored field-by-field.
Text content blocks are preserved verbatim on every migrated handler
so MCP clients without structured-content support keep working.
Additive change — the CLI still regex-parses text for now. CLI
migration to decodeStructured + --json lands in the follow-up PR.
Tests:
- New MacOSMCPTests.structuredContentPayloadsDecode exercises
every migrated tool against the real daemon and decodes each
response through the canonical DTO. Image-index references are
validated against the sibling content array.
- MCPIntegrationTests now depends on PreviewsCLI so @testable can
import DaemonProtocol.
- MCPTestServer.callToolResult + decodeStructured helpers added.
All 4 MacOSMCPTests pass (~56s).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Wave 2 PR 2/2. The daemon started emitting `structuredContent` in #117; this PR wires the CLI to decode those payloads and adds the `--json` output mode per the plan. Shared helpers in `MCPContentHelpers.swift`: - `Client.callToolStructured(name:arguments:)` — returns the full `CallTool.Result` including `structuredContent`. The SDK's tuple-returning `callTool` overload drops that field. - `Value.decode(_:)` — decode an MCP `Value` into a `Codable`. - `emitJSON(_:)` — write a pretty-printed, sorted-keys JSON document to stdout. Used by every `--json` mode. Regex parsers deleted (3 call sites): - `RunCommand.extractSessionID` - `SnapshotCommand.extractSessionID` - `VariantsCommand.extractSessionID` - `VariantsCommand.parseSuccessPreamble` - `VariantsCommand.parseFailurePreamble` Every site that needed the sessionID now decodes `PreviewStartResult.sessionID` from `structuredContent`. `VariantsCommand.captureVariants` rewrite: instead of walking the text/image content interleave with regex, decode `VariantsResult` and use each `VariantOutcomeDTO.imageIndex` to index into the sibling content array. The Critical ERROR-in-label bug from #109 is structurally unreachable now — outcome classification comes from a typed `status` field, not a substring match on prose. `--json` added to 7 read-oriented commands (per plan): - `run --detach --json` → full `PreviewStartResult`. - `snapshot --json` → `{ sessionID, outputPath, format, bytes }` synthesized client-side. - `variants --json` → `{ variants[], successCount, failCount }` with per-variant status/path/error. Files still written to disk. - `list --json` → `PreviewListResult` (client-side only; list does not hit the daemon). - `status --json` → `{ state, running, pid, socketPath }` synthesized client-side. - `simulators --json` → daemon's `SimulatorListResult` passthrough. - `elements --json` → `{ sessionID, elements }` envelope instead of the bare tree. Skipped on imperative commands (`stop`, `touch`, `configure`, `switch`, `kill-daemon`) per plan — nothing worth structuring on stdout. All 44 tests across 7 suites green. Smoke-tested end-to-end: - `run --detach --json` → emits full PreviewStartResult - `snapshot --json` → emits outputPath+bytes+format - `variants --json` → emits per-variant status/path - `status --json`, `list --json`, `simulators --json` work offline Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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…118) Wave 2 PR 2/2. The daemon started emitting `structuredContent` in #117; this PR wires the CLI to decode those payloads and adds the `--json` output mode per the plan. Shared helpers in `MCPContentHelpers.swift`: - `Client.callToolStructured(name:arguments:)` — returns the full `CallTool.Result` including `structuredContent`. The SDK's tuple-returning `callTool` overload drops that field. - `Value.decode(_:)` — decode an MCP `Value` into a `Codable`. - `emitJSON(_:)` — write a pretty-printed, sorted-keys JSON document to stdout. Used by every `--json` mode. Regex parsers deleted (3 call sites): - `RunCommand.extractSessionID` - `SnapshotCommand.extractSessionID` - `VariantsCommand.extractSessionID` - `VariantsCommand.parseSuccessPreamble` - `VariantsCommand.parseFailurePreamble` Every site that needed the sessionID now decodes `PreviewStartResult.sessionID` from `structuredContent`. `VariantsCommand.captureVariants` rewrite: instead of walking the text/image content interleave with regex, decode `VariantsResult` and use each `VariantOutcomeDTO.imageIndex` to index into the sibling content array. The Critical ERROR-in-label bug from #109 is structurally unreachable now — outcome classification comes from a typed `status` field, not a substring match on prose. `--json` added to 7 read-oriented commands (per plan): - `run --detach --json` → full `PreviewStartResult`. - `snapshot --json` → `{ sessionID, outputPath, format, bytes }` synthesized client-side. - `variants --json` → `{ variants[], successCount, failCount }` with per-variant status/path/error. Files still written to disk. - `list --json` → `PreviewListResult` (client-side only; list does not hit the daemon). - `status --json` → `{ state, running, pid, socketPath }` synthesized client-side. - `simulators --json` → daemon's `SimulatorListResult` passthrough. - `elements --json` → `{ sessionID, elements }` envelope instead of the bare tree. Skipped on imperative commands (`stop`, `touch`, `configure`, `switch`, `kill-daemon`) per plan — nothing worth structuring on stdout. All 44 tests across 7 suites green. Smoke-tested end-to-end: - `run --detach --json` → emits full PreviewStartResult - `snapshot --json` → emits outputPath+bytes+format - `variants --json` → emits per-variant status/path - `status --json`, `list --json`, `simulators --json` work offline Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Wave 2 PR 1/2 per plan in
/Users/obj-p/.claude/plans/tingly-twirling-crane.md. Additive: the daemon now emitsCallTool.Result.structuredContentalongside existing text content blocks. The CLI still regex-parses text in this PR; PR 2 wires the CLI to decode structured payloads and adds--json.What changed
New file:
Sources/PreviewsCLI/DaemonProtocol.swift— caseless-enum namespace holding Codable DTOs (PreviewStartResult,VariantsResult,SwitchResult,PreviewListResult,SimulatorListResult,SessionListResult, plus sharedPreviewInfoDTOandTraitsDTO).7 handlers migrated in
Sources/PreviewsCLI/MCPServer.swift:preview_start/preview_variants/preview_switch/preview_list/simulator_list/session_list— use the Codable init ofCallTool.Resultto encode the DTO intostructuredContent.preview_elements— the WDA accessibility tree is arbitrary nested JSON; parses the existing text payload intoValuedirectly rather than mirroring fields.Variants addressing: each
VariantOutcomeDTOcarriesimageIndex: Int?pointing into the siblingcontent: [Tool.Content]array, so the CLI can pair a label with its base64 image without regex-parsing the[N] <label>:preambles.Text content blocks are preserved verbatim on every handler — MCP clients without structured-content support keep working.
What's deferred
decodeStructured, add--jsonon 7 commands) — PR 2.preview_stop,preview_configure,preview_touch) — explicitly skipped per plan.Test plan
swift buildswift test --filter MacOSMCPTests— 4 tests pass (~56s), including the newstructuredContentPayloadsDecodethat exercises every migrated tool and asserts each payload decodes through its canonical DTO.VariantOutcomeDTO.imageIndexand confirms it points to an.imageblock in the sibling content array.Package change
MCPIntegrationTestsnow depends onPreviewsCLIso@testable importcan reachDaemonProtocol. This mirrors the existingPreviewsCLITeststarget.🤖 Generated with Claude Code