Refactor multisource plugin to use directive framework

[rjrodger]

Summary

Refactored the multisource plugin to leverage the new directive framework instead of implementing custom lexer matchers and token handling. This simplifies the codebase and improves maintainability by delegating parsing logic to the directive system.

Key Changes

• Removed custom lexer implementation: Eliminated the lexMode state machine, custom token matchers (msrcpath), and manual path parsing logic that handled quoted and unquoted paths
• Adopted directive framework: Replaced custom rule extensions with a DirectiveOptions configuration that defines the multisource directive behavior declaratively
• Simplified path resolution: Extracted resolveSource() into a standalone function that's called from the directive's action handler
• Enhanced rule handling: Implemented custom rule modifications through the directive's Custom callback to handle special cases like top-level references and map merging
• Added comprehensive tests: New test cases for path plugin integration, map merging with @path syntax, and top-level reference resolution

Implementation Details

• The directive framework handles tokenization and rule matching, eliminating ~150 lines of manual lexer code
• Map merging behavior (when @path appears in pair position) is now handled through parent rule inspection in the action handler
• Special handling for top-level @path references uses rule depth and custom flags to distinguish between value and map contexts
• The Custom callback modifies the val, map, and pair rules to inject directive-specific alternatives at appropriate positions

https://claude.ai/code/session_01UCcfE3sNcpkMr5eYdoR12u