* UN-2930 [FEAT] Add core plugin infrastructure

Introduce a generic, framework-agnostic plugin system that supports
Django, Flask, and Workers. This foundation enables dynamic loading
of plugins with metadata validation, singleton/non-singleton patterns,
and support for compiled extensions.

Key components:
- Generic PluginManager with plugin discovery and validation
- DjangoPluginManager wrapper for Django apps
- FlaskPluginManager wrapper for Flask apps
- Redis client enhancement (REDIS_USERNAME support)
- Plugin directory exclusions in .gitignore
- Development dependency: debugpy for debugging

This is the first PR in a series for UN-2930, establishing the
infrastructure needed for subscription usage tracking and other
plugin-based features.

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* Refactored plugin gitignore to avoid explicitly stating plugin names

* Added new plugin loading mechanism to BE
NOTE: Existing mechanism is left untouched to avoid breaking anything

* Addressed code rabbit's review comment

* Minor code rabbit comment addressed, updated docs on adding and using plugins

* misc: Updated plugin discovery to supported nested plugins upto 2 levels

* UN-2930 [FEAT] Enhance plugin_loader with required parameter validation

- Update plugin_loader docstring to clarify plugins_dir and plugins_pkg are required
- Add parameter validation with helpful ValueError message
- Include practical example showing correct usage pattern
- Improves developer experience with clear setup requirements

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Co-Authored-By: Claude <noreply@anthropic.com>

* UN-2930 [FIX] Add thread-safety to FlaskPluginManager singleton

- Add threading.Lock at class level to protect singleton instance
- Guard instance creation and state mutations with lock
- Prevent race conditions in multi-threaded Flask environments
- Ensure thread-safe initialization of app, plugins_dir, and plugins_pkg

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Co-Authored-By: Claude <noreply@anthropic.com>

* UN-2930 [REFACTOR] Merge nested conditions and simplify exception handling

- Merge nested if statements in FlaskPluginManager.getInstance() into single compound condition
- Remove redundant PermissionError from plugin_manager (OSError parent class covers it)

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Co-Authored-By: Claude <noreply@anthropic.com>

* [MISC] Refactor plugin loading for BE and prompt-service to use centralized get_plugin() mechanism (#1626)

Refactor plugin loading to use centralized get_plugin() mechanism

Replaced manual plugin loading implementations across backend, prompt-service,
and core modules with the new centralized get_plugin() function. This aligns
all plugin loading with the new infrastructure, reduces code duplication, and
simplifies maintenance. Removed obsolete loader files (subscription_loader,
modifier_loader, processor_loader) that are now replaced by get_plugin().

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* UN-2930 [FIX] Track subscription usage only for successful runs (#1620)

UN-2930 [FEAT] Implement subscription tracking for successful executions only

This PR implements the complete UN-2930 fix to track subscription usage
only for successful API calls and workflow executions.

Key changes:
- Add subscription usage tracking decorator for Django views
- Apply decorator to Prompt Studio index and answer-prompt operations
- Add workflow completion/failure handlers for defer/commit/discard pattern
- Implement batch tracking in workers for completed workflows
- Add platform-service plugin integration for subscription tracking
- Remove hardcoded SQL from platform-service, use plugin-based approach

Components:
1. Decorator (backend/utils/subscription_usage_decorator.py):
   - Auto-commits usage on success
   - Auto-discards usage on failure
   - Non-blocking error handling

2. Prompt Studio Integration:
   - Track usage for index_document()
   - Track usage for prompt_responder()

3. Workflow Integration:
   - Completion handler commits deferred usage for COMPLETED workflows
   - Failure handler discards all deferred usage

4. Workers Integration:
   - Batch commit for successful file executions
   - Calls internal API for efficient batch processing

5. Platform Service:
   - Plugin-based subscription tracking
   - Cleaner separation of concerns

This ensures usage is only recorded when operations actually succeed,
fixing the issue where failed operations were incorrectly tracked.

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* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update backend/configuration/config_registry.py

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
Signed-off-by: Chandrasekharan M <117059509+chandrasekharan-zipstack@users.noreply.github.com>

---------

Signed-off-by: Chandrasekharan M <117059509+chandrasekharan-zipstack@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>