Fix bugs found in deep code review (v7.3.0)

[jamesabel]

Summary

Fixes ~30 issues found in a deep code review of the whole library, spanning correctness bugs, error handling, concurrency, and resource lifecycle. Full test suite passes (91/91, moto mock) and mypy is clean.

Correctness

• dynamodb: upsert_item built an invalid UpdateExpression for multi-attribute items (missing commas) and failed on DynamoDB reserved words; now uses ExpressionAttributeNames/Values placeholders. Exceptions that were constructed but never raised (upsert_item(item=None), cache eviction) are now raised. scan_table no longer returns partial results on connection errors. Metadata-table mtime updates auto-create the metadata table (as documented) and are guarded consistently.
• s3: upload change-detection compared against get_sha512(), which never returns None, so non-awsimple objects always re-uploaded and the documented mtime fallback was dead code; now compares the raw .sha512. upload/download raise AWSimpleException after exhausting retries instead of silently returning False (so download_cached can no longer cache a failed download as success). download accepts str paths as documented. get_s3_object_url handles us-east-1 and uses the modern s3.{region} endpoint. bucket_exists honors the configured session/profile/LocalStack endpoint. get_s3_object_metadata uses a single head_object (dir() was ~3 API calls per object).
• dynamodb_miv: put_item bypassed metadata mtime updates (stale scan_table_cached results) and could silently overwrite items under concurrent writes; now updates metadata and uses a conditional put with retries.
• pubsub: old-queue cleanup could never match a queue (hash-prefix mismatch) — queue names are now channel-prefixed; make_name_aws_safe joins args with a separator so ("a","b") no longer collides with ("ab",). Main loop drains message queues each cycle (bursts previously throttled to ~1 message per 10 s). Threads survive transient AWS/JSON errors and log fatal failures instead of dying silently; module uses getLogger.
• sqs/sns: boto_error_to_string no longer crashes on BotoCoreError subclasses (the long-poll error handler crashed on the exact errors it was written to survive). Queue policies are merged rather than overwritten (subscribing to a second SNS topic no longer revokes the first). get_all_sqs_queues passes credentials through.
• aws: moto mock lifecycle is reference counted process-wide (env-var save/restore was GC-order dependent). test() calls STS GetCallerIdentity (the old check was offline-only, validated nothing, and raised PermissionError for services like logs); returns False on invalid credentials. LocalStack + resource_name=None no longer leaves .resource unset.
• logs: retries once with the expected sequence token instead of dropping the message.

Resource lifecycle / API polish

• functools.lru_cache/cache on instance methods (dynamodb, sns) pinned every instance for the process lifetime; replaced with per-instance caches.
• Single exception root: everything derives from AWSimpleException.
• dict_to_dynamodb preserves zero-length strings (supported by DynamoDB since May 2020).
• create_table key types are str/int/bytes; bool is rejected (DynamoDB "B" is binary).
• LRU cache eviction skips directories and measures free space on the cache directory's volume.

Behavior changes to note

• upload()/download() raise AWSimpleException on persistent failure instead of returning False.
• test() returns False for invalid credentials instead of passing an offline check.
• Pub/sub queue names changed format; stale queues from the old format age out via the now-functional remove_old_queues.
• dict_to_dynamodb("") returns "" instead of None.

Tests

• conftest holds a session-scoped AWSAccess so moto state persists across the suite deliberately (previously an accident of the lru_cache leak).
• scan_table_cached stamps its cache file with time.time(), fixing a Windows clock-granularity flake with only a ~5 ms natural margin.
• pytest scoped to test_awsimple via pyproject.toml so bare pytest doesn't execute examples/*_test.py at import time.
• Version bumped to 7.3.0.

🤖 Generated with Claude Code