Add incremental tile and entry-bundle writers

[achamayou]

Summary

Part 2 of the tiled-storage series; follow up to merged #52.

• add TileWriterT for progressive complete-tile production and all-level roll-ups;
• add EntryBundleWriterT for optional complete raw-entry bundles;
• recover from a caller-validated contiguous prefix without trusting sparse high-index files;
• preserve immutable/idempotent writes while repairing malformed interior files;
• retain and exercise durability retry behavior across writer and store instances;
• specify write, resume, ownership, and entry-bundle semantics.

Series

1. Add durable tlog-tiles storage primitives #52 — tile formats and durable storage (merged)
2. This PR: incremental writers
3. tile-backed proof generation
4. TiledTree lifecycle wrapper
5. user documentation and performance coverage

Validation

• tiles_store
• tiles_writer
• tiles_entries
• header clang-tidy

[Copilot]

Pull request overview

This PR extends the tiled-storage stack (follow-up to #52) by adding incremental writers for producing complete hash tiles across levels (TileWriterT) and optional raw-entry bundles (EntryBundleWriterT), plus corresponding tests and design documentation updates.

Changes:

• Added TileWriterT and EntryBundleWriterT to incrementally persist newly-complete tiles/bundles while preserving immutability/idempotency and supporting bounded recovery.
• Added new integration-style tests (tiles_writer, tiles_entries) and expanded tiles_store doctest coverage for sync-failure retry semantics in the writer.
• Updated the tlog-tiles design document to specify writer/resume semantics and expected tile counts.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/tiles_writer.cpp	Adds end-to-end tests for incremental tile writing, resume behavior, and bounded recovery.
test/tiles_store.cpp	Adds doctest cases validating writer behavior across injected directory-sync failures.
test/tiles_entries.cpp	Adds end-to-end tests for incremental entry-bundle writing, corruption repair on resume, and bounded recovery.
test/CMakeLists.txt	Registers the new tiles_writer and tiles_entries tests with CTest.
merklecpp_tiles.h	Introduces perfect_root, TileWriterT, and EntryBundleWriterT APIs and implementations.
doc/design/tlog-tiles.md	Documents the new writer APIs and their incremental/resume semantics within the tlog-tiles design.

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[cjen1-msft]

I think this is good.

Agent comments, but no blockers here.

• The validation is noted as being structural only ie not checking for disk corruption
  • This should be alright.
• Test for a level 2 roll-up possibly useful?
• sha-384 or sha-512 could be nice to also test

[achamayou]

Test for a level 2 roll-up possibly useful?
sha-384 or sha-512 could be nice to also test

Added both cases to tiles_writer: a full level-2 roll-up over 256 level-1 tiles, and an OpenSSL-gated SHA-384 writer test that verifies the level-1 tile and tiled root against Tree384.