[HTHou]

Summary

Stacked on #866, targeting codex/tsfile-tde-page-aead rather than develop.

• Add provider-defined encoded-size calculation and bounded, read-only candidate plaintext-length parsing.
• Preserve fixed-overhead defaults for existing GCM providers and the existing size-only context overload.
• Route direct, chunk, and lazy page readers through the encoded-body overload before rebuilding AAD.
• Treat parsed lengths as untrusted framing until page authentication succeeds, and validate encoded-size consistency.
• No file-version, encryption-header-version, AAD-version, or existing GCM encoding changes; no CBC algorithm implementation in TsFile.

Validation

39 focused tests passed across PageCryptoContextTest, PageBodyEncoderTest, FileEncryptionHeaderTest, PageAeadReaderLifecycleTest, and EncryptionProviderRegistryTest.
Coverage includes variable-length padded framing, direct/sliced buffers, framing tampering, compression, aligned/non-aligned queries, and existing fixed-expansion lifecycle behavior.

Motivation

Allows external providers to support padded authenticated encodings such as CBC plus HMAC without making storage code infer plaintext length by subtracting a fixed overhead.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.