[Feature]: Prove incremental and full graph builds are equivalent

[Baziar]

Problem statement

Workspai already reuses unchanged project/provider output. The remaining risk
is correctness: deletes, renames, shared contracts, or provider-version changes can
leave stale entities or proofs unless incremental output is continuously checked
against a clean build.

Proposed solution

Current foundation

• incremental Workspace Model builds;
• incremental-project-cache graph provider protocol;
• add/change/cache invalidation tests;
• full rebuild fallback and source fingerprints;
• PCC re-observation coverage for deletion, Graph overlay aliases, and artifact
  resurrection detection.

Remaining work

Turn equivalence into a release invariant using the shared provider corpus and randomized
mutation sequences. Compare semantic content while excluding only declared
run-local timestamps/metadata.

Acceptance criteria

• Add, edit, delete, rename, and repeated dirty edits are covered.
• Cross-file, shared-schema, and cross-project invalidation are covered.
• Incremental output equals a clean full build for entities, relations, proofs, and omissions.
• Provider/schema/normalizer version changes invalidate the correct scope.
• Incomplete Git evidence reports a fallback instead of false reuse.
• Cancellation preserves the previous valid graph atomically.
• JSON explains reused, rebuilt, and full-fallback scopes.
• Randomized mutation runs pass on Linux, macOS, and Windows.

Completion evidence

Publish semantic diff output for the fixed corpus, randomized seed/reproduction
commands, and a measured one-file change on a 10,000-file fixture. Correctness is
the blocker even if a full build is temporarily faster.

Alternatives considered

The following alternatives or adjacent concerns are intentionally outside this issue:

• redesigning the existing cache protocol;
• performance claims before correctness passes;
• distributed graph storage.

Expected impact

Large workspaces can reuse unchanged graph evidence without risking stale
entities, relations, or proofs after source and provider changes.

[github-actions]

Hey @Baziar — welcome to Workspai! 👋

Thanks for taking the time to open your first issue. Clear reports and focused ideas help us make Workspai more useful for developers and AI tools working across real software workspaces.

A maintainer will review the scope and labels. If you would like to work on this issue yourself, leave a comment and we’ll help you find the relevant contracts, code, and tests.

Glad to have you here.