[bitborne]

Description

Converges Mooncake Store's existing S3 client environment settings under a private S3ClientConfig as part of #3809.

• Groups the eleven existing MOONCAKE_AWS_* variables in the common environment catalog using their semantic string, boolean, and int64_t types.
• Loads the values through typed Environ::ReadOr() and caches the resolved config once from S3Helper::InitAPI() for the process lifetime.
• Removes the S3-specific getters, backing fields, constructor reads, and singleton-coupled test from the global Environ object.
• Preserves all existing variable names, defaults, literal string behavior, shared boolean/integer parsing, invalid-value warnings, explicit endpoint/bucket/region argument precedence, credential redaction, and restart/reinitialization caching behavior.
• Keeps checksum-mode parsing beside the AWS SDK types. An unset or explicitly empty Mooncake checksum setting still leaves the AWS SDK default unchanged, preserving the compatibility correction reviewed in [Store] Externalize S3 client config via environment variables #2649.
• Adds focused config tests for defaults, all populated settings, explicitly empty strings, invalid typed-value fallbacks and diagnostics, environment restoration, and independent loader reads.

Open PR #1538 is a broad cross-module migration toward a larger global Environ singleton. This PR is the narrow Store-only owner migration required by the current #3809 rules: it removes S3-specific global state, keeps the config header private, and does not change Transfer Engine or other component settings.

Open PR #2205 proposes a new checksum compatibility switch and still targets the pre-#3587 S3 helper path. This PR does not introduce that variable or adopt its behavior; if #2205 is revived, its behavior can be layered onto S3ClientConfig separately.

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Mooncake Conductor (mooncake-conductor)
• Reshard (mooncake-reshard)
• Mooncake EP (mooncake-ep)
• Mooncake PG (mooncake-pg)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• Common (mooncake-common)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Performance improvement
• Other

How Has This Been Tested?

Test commands:

cmake -S . -B build -DBUILD_UNIT_TESTS=ON -DSTORE_USE_REDIS=ON -DWITH_STORE_RUST=OFF -DBUILD_EXAMPLES=OFF -DBUILD_BENCHMARK=OFF
cmake --build build --target s3_client_config_test mooncake_master -j16
cmake --build build --target local_file_snapshot_config_test local_file_snapshot_object_store_test -j16
ctest --test-dir build --output-on-failure -R '^(environ_test|s3_client_config_test|local_file_snapshot_config_test|local_file_snapshot_object_store_test)$'
pre-commit run --files mooncake-common/include/environ.h mooncake-common/include/environment_variables.h mooncake-common/src/environ.cpp mooncake-common/tests/environ_test.cpp mooncake-store/src/CMakeLists.txt mooncake-store/src/common/s3_helper.cpp mooncake-store/src/config/s3_client_config.cpp mooncake-store/src/config/s3_client_config.h mooncake-store/tests/CMakeLists.txt mooncake-store/tests/s3_client_config_test.cpp
./scripts/code_format.sh --check --changed-lines --base kvcache/main

The Store master executable and focused config test build successfully. All four selected tests pass, touched-file pre-commit passes with pre-commit 3.7.1, and the post-commit changed-lines check passes with clang-format 20.1.8.

The local environment does not have the AWS SDK installed, so the conditionally compiled s3_helper.cpp path was not compiled locally. The SDK-independent S3ClientConfig is compiled into mooncake_master; AWS-enabled CI remains responsible for compiling the consumer path.

Test results:

• Unit tests pass
• Integration tests pass (if applicable)
• Manual testing done (describe below)

Checklist

• I have performed a self-review of my own code
• I have formatted my code using ./scripts/code_format.sh
• I have run pre-commit on the files changed in this PR and all hooks pass
• I have updated the documentation (if applicable)
• I have added tests to prove my changes are effective
• For changes >500 LOC: I have filed an RFC issue

No documentation update is needed because this ownership refactor does not change the supported environment-variable contract. The change is below 500 LOC, including tests, so no RFC is required.

AI Assistance Disclosure

• No AI tools were used
• AI tools were used (specify below)

Codex assisted with ownership and lifecycle inventory, compatibility analysis, implementation, focused tests, verification, overlap checks, and pre-submission review. The human submitter reviewed every changed line and can defend the change end-to-end.

[Aionw]

Can we use std::chrono::milliseconds instead of int64_t here?

[Aionw]

Same as above

[Aionw]

LGTM