Problem

In distributed mode, routing a directory-based model to a remote NATS worker fails with:

staging model files for node dgx-spark: staging model file:
uploading /models/qwen3-tts-cpp to node ...:
Put ".../v1/files/models/qwen3-tts-cpp/qwen3-tts-cpp": read /models/qwen3-tts-cpp: is a directory

stageModelFiles treats every model path field (ModelFile, MMProj, Tokenizer, …) as a single regular file. file_stager_http.go:doUpload does os.Open(localPath) and streams the fd as the HTTP PUT body. Opening a directory succeeds, but reading its fd returns EISDIR ("is a directory").

Models whose parameters.model points at a directory of files hit this. Example: qwen3-tts-cpp ships weights + tokenizer:

/models/qwen3-tts-cpp/qwen3-tts-0.6b-f16.gguf
/models/qwen3-tts-cpp/qwen3-tts-tokenizer-f16.gguf

# qwen3-tts-cpp.yaml
parameters:
    model: qwen3-tts-cpp   # a directory

Single-file models (e.g. parakeet → parakeet-cpp/tdt-0.6b-v3-f16.gguf) are unaffected, so this surfaces specifically on multi-file pipelines — notably the realtime TTS stage, which fails to load on any worker that doesn't already have the files locally.

Fix

stageModelFiles now detects when a path field is a directory and stages each contained file individually via a new stageDirectory helper:

• filepath.WalkDir the directory, EnsureRemote each file using the existing StagingKeyMapper (structure-preserving keys, so files land under one tracking-key dir on the worker).
• Rewrite the field to the remote directory path and derive ModelPath as before, so the backend's ModelFile resolves correctly on the worker.
• countStageableFiles expands directories when computing the staging progress total, so the tracker doesn't exceed 100%.

Single-file staging is unchanged.

Tests

• New router_dirstage_test.go: a directory ModelFile stages each contained file (not the directory path). Verified RED before the fix, GREEN after.
• Full core/services/nodes suite passes (ok ... 160s).