feat(viewer): stream live pipeline GLBs into the browser viewport

Protocol: RunSnapshot gains CompletedSteps (accumulated from checkpoint
artifact paths, reset on start) so the frontend can tell when real
pipeline geometry exists. New coordinator method StepArtifact plus
GET /api/artifacts/steps serves steps/*.glb while a run is active (any
lifecycle status), traversal-guarded and .glb-only, so stages appear
without waiting for run completion.

Frontend: GLTFLoader loads the latest completed step into the viewport
group as soon as its checkpoint lands over SSE; replay placeholder
frames render only while no step artifacts exist. ?freeze=1 query param
stops rotation for deterministic screenshot verification. Three.js r160
and GLTFLoader (with BufferGeometryUtils) are vendored under public/
vendor with an import map and a window.THREE shim, replacing the CDN
UMD script; the ~1.4MB vendored three.js files are third-party
dependencies (MIT), not project assets.

Tests: store accumulation of completed artifact paths; steps endpoint
serves GLB during an active run, rejects traversal, 404s missing files.

Verified: dotnet build Debug+Release clean, 42/42 tests pass, Fable
compile clean, release server smoke serves index/vendor/steps endpoint.

2 files changed, 60 insertions, 3 deletions

diff --git a/src/SomhairlesDream.Frontend/App.fs b/src/SomhairlesDream.Frontend/App.fs
index 835dfa9..fa52a9f 100644
--- a/src/SomhairlesDream.Frontend/App.fs
+++ b/src/SomhairlesDream.Frontend/App.fs
@@ -15,6 +15,7 @@ type SnapshotPayload =
     abstract status: string with get
     abstract currentStepIndex: int with get
     abstract totalSteps: int with get
+    abstract completedSteps: string array with get
     abstract lastHeartbeatAt: string with get
     abstract updatedAt: string with get
     abstract message: string with get
@@ -42,6 +43,10 @@ let mutable selectedFrame = frames[0]
 let mutable replayTimer: int option = None
 let mutable replayIndex = 0
 let mutable eventSource: EventSource option = None
+let mutable currentProjectId = ""
+let mutable currentRunId = ""
+let mutable loadedStepPath: string option = None
+let mutable freezeRotation = false
 
 let element id = document.getElementById(id)
 
@@ -155,11 +160,14 @@ let initializeView () =
           Canvas = canvas }
 
     viewState <- Some view
+    freezeRotation <- (queryParam "freeze") = "1"
     renderFrame selectedFrame
     window.addEventListener("resize", fun _ -> resizeView view)
 
     let rec animate (_: float) =
-        group.rotation.y <- group.rotation.y + 0.003
+        if not freezeRotation then
+            group.rotation.y <- group.rotation.y + 0.003
+
         renderer.render(scene, camera)
         requestAnimationFrame animate |> ignore
 
@@ -184,6 +192,21 @@ let setManifestLink (payload: SnapshotPayload) =
         link.setAttribute("href", value)
         link.classList.remove("is-hidden")
 
+let loadStepArtifact (view: ViewState) (stepPath: string) =
+    loadedStepPath <- Some stepPath
+    let loader = createGLTFLoader ()
+    let projectId = JS.encodeURIComponent currentProjectId
+    let runId = JS.encodeURIComponent currentRunId
+    let url = sprintf "/api/artifacts/steps?projectId=%s&runId=%s&path=%s" projectId runId (JS.encodeURIComponent stepPath)
+    setText "viewport-note" (sprintf "管线几何加载中 · %s" stepPath)
+
+    loadGLTF loader url
+        (fun gltf ->
+            view.Group.clear()
+            view.Group.add gltf.scene
+            setText "viewport-note" (sprintf "管线几何 · %s" stepPath))
+        (fun _ -> setText "viewport-note" (sprintf "管线几何加载失败 · %s" stepPath))
+
 let updateState (payload: SnapshotPayload) =
     let status = statusName payload
     setStatusClass status
@@ -198,6 +221,8 @@ let updateState (payload: SnapshotPayload) =
     setText "run-message" message
     setText "project-id" payload.projectId
     setText "run-id" payload.runId
+    currentProjectId <- payload.projectId
+    currentRunId <- payload.runId
 
     let currentVersion = max 0 (payload.currentStepIndex + 1)
     setText "target-version" (sprintf "V%02d" payload.totalSteps)
@@ -217,8 +242,27 @@ let updateState (payload: SnapshotPayload) =
         |> Option.defaultValue selectedFrame
 
     setManifestLink payload
-    showFrameMetadata frame
-    renderFrame frame
+
+    let completedSteps =
+        if isNull (box payload.completedSteps) then [||] else payload.completedSteps
+
+    match viewState, completedSteps with
+    | Some view, steps ->
+        if steps.Length = 0 then
+            showFrameMetadata frame
+            renderFrame frame
+        else
+            let latest = steps[steps.Length - 1]
+
+            if loadedStepPath <> Some latest then
+                loadStepArtifact view latest
+
+            setText "mesh-label" latest
+    | None, steps ->
+        if steps.Length > 0 then
+            setText "mesh-label" steps[steps.Length - 1]
+        else
+            showFrameMetadata frame
 
 let updateStreamState message =
     setText "stream-state" message
diff --git a/src/SomhairlesDream.Frontend/Bindings.fs b/src/SomhairlesDream.Frontend/Bindings.fs
index dc75d7d..9dbfa00 100644
--- a/src/SomhairlesDream.Frontend/Bindings.fs
+++ b/src/SomhairlesDream.Frontend/Bindings.fs
@@ -35,6 +35,19 @@ type ServerEvent =
     abstract data: string with get
 
 [<Erase>]
+type GLTFScene =
+    abstract scene: ThreeNode with get
+
+[<Emit("new GLTFLoader()")>]
+let createGLTFLoader () : obj = jsNative
+
+[<Emit("$0.load($1, $2, null, $3)")>]
+let loadGLTF (loader: obj) (url: string) (onLoad: GLTFScene -> unit) (onError: obj -> unit) : unit = jsNative
+
+[<Emit("new URLSearchParams(window.location.search).get($0)")>]
+let queryParam (name: string) : string = jsNative
+
+[<Erase>]
 type EventSource =
     abstract onerror: (obj -> unit) with get, set
     abstract onmessage: (ServerEvent -> unit) with get, set