fix(be): Add max history index proto fields - #23831

Summary by CodeRabbit

• New Features
  • Base image information now includes ordered build-history entries, including instructions that did not create a content layer.
  • Image metadata can distinguish the last recorded build-history entry from the last content layer, preserving empty history lines when comparing base and derived images.

The storage schemas now record ordered base-image history entries, including entries without content blobs. BaseImageInfo adds an optional index for the final base history entry when base history is a strict prefix of child history.

Changes: Base-image history

Layer / File(s)	Summary
Store base-image history proto/storage/base_image.proto, proto/storage/base_image_repository.proto	BaseImage and BaseImageTag gain ordered history fields that use BaseImageHistoryEntry. Each entry contains an instruction, a value, and an empty-content flag. The fields are excluded from search and SQL mappings.
Define the history boundary proto/storage/image.proto	BaseImageInfo adds presence-aware max_history_index. The documentation defines its use when base history is a strict prefix of image history. When unset, Dockerfile-line filtering must not cut history. max_layer_index refers to the last base content-blob manifest index.

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Suggested reviewers: ajheflin, alkmim

Merge Risk: Minimal · previous review 80048

The schema adds history storage and an optional boundary without changing filtering. No merge-blocking risk is identified.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly identifies the primary change: adding max history index fields to the backend proto definitions. It is concise and related to the changeset.
Description check		The description explains the purpose, scope, data model, runtime impact, documentation status, testing status, and validation method. It also explains why no new tests were added for this schema and g…
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the purpose, scope, data model, runtime impact, documentation status, testing status, and validation method. It also explains why no new tests were added for this schema and generated-code-only change.

Full details: Docstring Coverage

Explanation

No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 0 files. (3 skipped: 3 unsupported.)

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- Coverage   52.61%   52.57%   -0.04%     
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- Hits        93642    93574      -68     
- Misses      76140    76187      +47     
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