Bug fixes

[gmac]

PR Summary

This branch fixes several planning, execution, and shaping edge cases and adds coverage around them. Audit and fixes performed by Codex.

Changes

• Fix planner step coalescing so reused entrypoints keep their original step index and merge variables from later selections.
• Preserve variables used in list arguments, nested input values, inline fragment directives, and fragment spread directives.
• Preserve fragment directives when fragment spreads are rendered into inline fragments.
• Support mutation root __typename planning through the supergraph location.
• Fix executor root-source batching so multiple same-location nested root ops all execute instead of silently completing only the first.
• Add shared executor path traversal for origin object collection and error repathing across root and resolver sources.
• Fix resolver-source error repathing for nil siblings and nested list origins.
• Keep generated resolver variables local to each document build to avoid stale variables leaking between batches.
• Fix shaper null bubbling for scalar lists, nested required lists, and concrete inline fragments without exported typenames.
• Cache possible type-name lookups during shaping.
• Add planner benchmark task and loosen development dependency upper bounds.
• Bump version to 1.7.4.