Relax server schema gate to unblock sync with older YAOS plugin schemas

[Copilot]

Current server deployments can reject sync with This server requires schema version 3 or newer even when clients are on the latest plugin release path, creating a hard compatibility stop. This change redefines server schema compatibility as a bounded range instead of an exact minimum-only gate.

• Schema compatibility change

  • Lowered SERVER_MIN_SCHEMA_VERSION from 3 to 1 in server/src/version.ts.
  • Kept SERVER_MAX_SCHEMA_VERSION at 3 so the server still advertises the current schema ceiling.

• Guard logic updated for range semantics

  • Updated scripts/guard-schema-version.mjs to enforce:
    • SERVER_MAX_SCHEMA_VERSION === EXPECTED_SCHEMA_VERSION
    • SERVER_MIN_SCHEMA_VERSION <= EXPECTED_SCHEMA_VERSION
    • SERVER_MIN_SCHEMA_VERSION <= SERVER_MAX_SCHEMA_VERSION
  • This preserves drift protection while allowing intentional backward-compatible windows.

• Engineering docs aligned with runtime behavior

  • Updated docs/engineering/schema-version-guard.md to reflect range-based validation and new pass/fail expectations.

// server/src/version.ts
export const SERVER_MIN_SCHEMA_VERSION = 1;
export const SERVER_MAX_SCHEMA_VERSION = 3;