Fix Hydra config loading to support custom config paths and prevent reinitialization errors

[anujonthemove]

This PR updates the build_sam2() function to use Hydra’s recommended initialize_config_dir() pattern, resolving configuration loading issues and enabling flexible, reusable model initialization.

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✅ Key Changes:

• Replaces compose()-only approach with initialize_config_dir() to support loading configs from custom local paths (config_root).
• Adds check and clearing of existing Hydra state to prevent GlobalHydra already initialized runtime errors.

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📌 How can this help:

• Custom Config Support:
  The original code assumed Hydra could locate the config via its default search path, which failed for local or container-mounted configs. This change enables users to explicitly specify the root directory for config files.

• Hydra Reinitialization Error Fix:
  In scripts or interactive sessions (e.g., notebooks, demos), Hydra throws a GlobalHydra is already initialized error when reused. This patch handles such cases safely.

• Improved Portability:
  The updated implementation ensures reliable config loading across environments, including containers, distributed jobs, and non-Hydra CLI contexts.

[Copilot]

Pull Request Overview

This PR fixes Hydra config loading issues by using initialize_config_dir to support custom config paths and prevent reinitialization errors.

• Implements proper Hydra initialization by clearing GlobalHydra state before configuration loading.
• Adds a config_root parameter in build_sam2 for user-specified configuration directory paths.
• Updates the demo script to match the new local configuration path structure.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
sam2/build_sam.py	Refactors build_sam2 to use initialize_config_dir, clears GlobalHydra if already initialized, and adds a config_root parameter.
grounded_sam2_local_demo.py	Updates SAM2_MODEL_CONFIG to reflect the new local config path format.

Comments suppressed due to low confidence (1)

sam2/build_sam.py:118

• The variable 'config_file' is referenced in the compose() call but is not defined in the function signature. Consider adding 'config_file' as an explicit parameter to avoid potential runtime errors.

cfg = compose(config_name=config_file, overrides=hydra_overrides_extra)