CLI: EISDIR error when outputDirectory is a directory in single-file mode

[nathanacurtis]

Bug

When outputDirectory is set to ./specs in specs.config.yaml and that path already exists as a directory (e.g. from a prior --split-components run), running specs generate without --split-components or -o fails with:

Error: Failed to write file: EISDIR: illegal operation on a directory, open '.../specs'

Expected behavior

The CLI should detect the directory conflict and either:

1. Append a default filename (e.g. {outputDirectory}/{alias}.yaml) when the path is a directory
2. Provide a clear error message explaining the conflict and suggesting -o or --split-components

Steps to reproduce

1. specs init and configure a source
2. specs fetch && specs scan — select components
3. specs generate --split-components — creates specs/ directory with per-component files
4. specs generate — fails with EISDIR

Context

• CLI version: 0.11.0
• The outputDirectory config value serves dual purpose: as a directory for split modes and as a file path for single-file mode. This ambiguity causes the conflict.

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