feat(graphql): method-level alias support with three-state mutation feedback (fixes #140)

[allmonday]

Summary

Fixes #140 and delivers full specs/023: method-level GraphQL aliases on both query paths, with per-call three-state mutation feedback and a federation wire gate that keeps member services alias-free.

Root cause fixed: QueryParser._parse_selection_set keyed sub_fields by field name, so same-name aliased invocations overwrote each other — N aliased add_node calls executed once with errors: []. Keys are now response keys (alias or name); lookups resolve via FieldSelection.name.

What you get

mutation { MindmapService {
  n1: add_node(content: "one")   { display_id }
  n2: add_node(content: "two")   { display_id }
  n3: add_node(content: "three") { display_id }
} }

• Queries: aliased same-method fan-out with different args — each alias is an independent call, keyed by alias, projections isolated per alias; a failing alias nulls only itself (QUERY_FAILED), siblings unaffected
• Mutations: serial in declaration order, N aliases = N side effects (no execution-level dedup). On failure: prior results survive, failing key nulls with MUTATION_FAILED, later keys are skipped and marked SKIPPED_PRIOR_FAILURE (fail-stop)
• Conflict detection: duplicate response keys (alias repeats, alias/field collisions, plain duplicate fields — no spec field-merging) raise ALIAS_CONFLICT before any method executes
• Federation boundary: the wire never carries aliases — _wire_render_name renders original field names (alias-gated: hand-built resolver trees reuse name for the target TYPE name, so only aliased nodes substitute). Members need zero changes
• Out-of-scope aliases reject loudly (never silently): nested-field renames, federation remote-relationship fields, CLI --select
• QueryParser.validate_no_aliases() keeps its semantics as an optional user-side guard; nexusx no longer calls it internally

Behavior changes to note (6.2.0, minor)

• Same-name duplicate selections previously "last one wins" silently → now a loud ALIAS_CONFLICT
• entity-first: one failing method no longer nulls the whole entity group — the failed key nulls with RESOLVER_ERROR, sibling results survive; mutation groups fail-stop (per specs/023 clarify Q1, both paths unified)
• compose: execution-time failures (method body, coercion, missing FromContext) are per-field (QUERY_FAILED) instead of nulling the whole response; planning errors still fail fast

Validation

• Full suite 1637 passed, 6 skipped (baseline 1605 + 32 new, zero regressions); ruff check src/ clean
• Issue Mutation fields with aliases are silently collapsed — only the last one executes #140's original scenario covered end-to-end (6 aliased add_node → 6 nodes, 6 keyed results)
• Federation matrices (β materialized / γ DTO / paginated) green incl. wire alias-free assertions
• Spec artifacts under specs/023-gql-alias-support/ (spec/plan/research/contracts/quickstart/tasks, all 🇨🇳 per project convention); user guide at docs/guide/graphql-aliases.md

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