Detect struct fields removed from the spec but left in models.rs (#237)

[sdairs]

Closes #237.

Problem

OpenAPI drift detection was one-directional for fields (spec → code). It caught fields added to the spec that are missing from models.rs and optionality flips, but not the reverse: a field removed from the live spec yet still present as a struct field. A model that is a superset of the spec passed every field check — exactly how the stale storageSize fields in #235/#236 slipped through.

Change

Adds the code→spec mirror of the existing missing-field check, matching the missing/extra split already used for client methods (assert_client_operation_coverage), and remediates the findings it surfaces so the model matches the vendored snapshot.

Detector

• spec_coverage_test.rs: assert_no_extra_struct_fields + struct_fields_have_no_extras_vs_spec (snapshot) and struct_fields_have_no_extras_vs_live_spec (live, #[ignore]). Adds an EXTRA_FIELD_EXEMPTIONS allowlist — analogous to OPTIONALITY_EXEMPTIONS / NON_OPENAPI_CLIENT_METHODS — with stale-entry detection. Schemas with no/empty properties are skipped so composition/marker schemas don't flag every field.
• check-openapi-drift.py: check_extra_fields reverse pass + parse_extra_field_exemptions (reads the same Rust constant), surfaced as a new "Extra Struct Fields" report section and summary row.
• AGENTS.md: documents the now-bidirectional field coverage and the EXTRA_FIELD_EXEMPTIONS allowlist.

Remediation

The detector surfaced 5 stale fields against the snapshot; all are fixed, not exempted, so EXTRA_FIELD_EXEMPTIONS stays empty.

Schema	Field(s) removed	Spec allows
PostgresServicePatchRequest	name, provider, region, postgresVersion	size, haType, tags
ScimEnterpriseManager	$ref	displayName, value

• PostgresServicePatchRequest is live CLI surface — same class of stale field as the storageSize cleanup in Remove storageSize from Postgres create/update requests #235/Remove storageSize from Postgres create/update requests #236. The postgres update command loses the matching --name/--region/--provider/--pg-version flags (keeps --size/--ha-type/--add-tag/--remove-tag); PostgresUpdateOptions, the postgres_update handler, the main.rs match arm, the parse/write-command tests, and the README update example are updated accordingly.
• ScimEnterpriseManager.$ref was a code-only SCIM attribute absent from the ClickHouse spec, with no usages.
• Library update_postgres_service mock test rewritten to patch size instead of name.

The live-spec-only findings (seekSnapshot on the two PubSub sources) are out of scope — they aren't in the vendored snapshot this PR aligns to; they'll be picked up by the live drift run / snapshot refresh.

Verification

• struct_fields_have_no_extras_vs_spec now passes — all 9 snapshot spec-coverage tests green; the 8 live-spec tests stay #[ignore].
• Allowlist proven both ways: a real entry is suppressed (NOTE: … exempted), a bogus entry fails as stale.
• Drift script renders the new section/summary row; script and test agree on the same findings.
• cargo build, cargo clippy --all-targets, and the full clickhousectl + clickhouse-cloud-api test suites pass; all integration targets compile.

🤖 Generated with Claude Code

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Note

Medium Risk
Removes postgres update flags and patch request fields users may still rely on; changes are spec-aligned but are a breaking CLI/API-model surface for Postgres metadata updates.

Overview
Adds bidirectional OpenAPI field coverage so drift detection catches Rust struct fields that no longer exist in the spec, not only missing spec properties. spec_coverage_test.rs gains assert_no_extra_struct_fields with snapshot and live-spec tests plus an empty EXTRA_FIELD_EXEMPTIONS allowlist (stale-entry checks). check-openapi-drift.py mirrors this with check_extra_fields, exemption parsing, and an Extra Struct Fields report section.

Remediation removes five stale fields surfaced by the new check: PostgresServicePatchRequest drops name, provider, region, and postgresVersion; ScimEnterpriseManager drops $ref. The cloud postgres update CLI is narrowed to match the patch schema—--name, --region, --provider, and --pg-version are removed; updates use --size, --ha-type, and tag flags. README, library mock tests, and CLI parse/write tests follow the same shape.

AGENTS.md documents bidirectional field coverage and extra-field exemptions.

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