feat: harden config diff and apply semantics

[nobodyiam]

Summary

• define config synchronization as a conservative merge: create and update source keys while preserving target-only keys; reject unexpected server-side deletes
• capture the complete paginated source snapshot inside config apply, derive a detailed redacted plan, and compare the same source plus fully paginated target state before synchronization to detect observable stale changes
• return stable source/target scopes and create/update/delete/unchanged counts without exposing config values
• skip the synchronize request for empty-source and no-op plans, returning a deterministic no-op success result
• validate pagination completeness and target identity, reject unsupported cross-namespace apply, and redact config-sync HTTP error bodies
• document merge, two-stage approval, advisory diff, no-op, stale-plan, pagination, and the current synchronize contract non-atomic check/write limitation in both READMEs

Testing

• cargo fmt --check
• cargo test (177 tests passed)
• cargo clippy --all-targets --all-features -- -D warnings
• git diff --check
• Apollo all-in-one smoke at localhost:8070 using LOCAL/default and LOCAL/cli5668-target: preview reported create=1, update=1, delete=0, unchanged=1; apply preserved the target-only key; repeated apply returned result=no-op

Refs apolloconfig/apollo#5668
Refs apolloconfig/apollo#5626

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-30T11:54:04.042760Z	ae09d36	New commits

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[Copilot]

Pull request overview

This PR hardens the config diff / config apply workflow by defining and enforcing conservative merge semantics, improving safety around stale plans, pagination completeness, and redaction of config values and error bodies.

Changes:

• Implement conservative merge assessment and apply flow with stable scopes + create/update/delete/unchanged counts, plus deterministic no-op handling.
• Add stricter pagination validation for source snapshots and stronger target identity validation for diff/apply.
• Update CLI help + READMEs and expand OpenAPI/CLI tests for the new contract and redaction behavior.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/openapi.rs	Updates and adds tests for redacted outputs, new diff/apply semantics, no-op, stale-plan, pagination validation, and error-body redaction.
tests/cli.rs	Verifies updated --help text for conservative merge semantics.
src/mutation.rs	Extends mutation plan metadata to include config-sync strategy/behavior and change counts; exposes MutationScope::render_table.
src/http.rs	Adds an OpenAPI request mode that redacts error bodies entirely to prevent leaking secrets from server errors.
src/error.rs	Introduces a structured stale_plan error variant with conflict categorization and operation context.
src/command.rs	Implements snapshot capture, diff assessment parsing/validation, stale-plan checks, no-op handling, and new structured diff/apply outputs.
src/cli.rs	Updates config diff/apply help text to document conservative merge behavior and no-op/deletion expectations.
README.zh.md	Documents the conservative merge contract, output fields, no-op/stale-plan behavior, and redaction guarantees (ZH).
README.md	Documents the conservative merge contract, output fields, no-op/stale-plan behavior, and redaction guarantees (EN).

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