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-# Incremental builds: future work
-
-Recorded after the Separate Compilation README review, 2026-10-24. This is a
-design outline, not a description of implemented incremental builds.
-
-## Current gap
-
-`CompUnit` decides whether to reuse an object when the unit is discovered. It
-checks its source timestamp and its dependencies' existing object timestamps.
-It does not settle the whole dependency graph before accepting saved IR.
-
-For example:
-
-1. A depends on B and has inlined some of B.
-2. B's source changes, leaving B's object unchanged.
-3. A client discovers A. A's check sees the old B object and accepts A's object.
-4. Later discovery notices that B needs rebuilding, without reconsidering A.
-
-The compiler can therefore reuse code based on stale bodies or constants.
-An unchanged public signature is insufficient: Simple imports implementation
-details for optimization as well as declarations for type checking.
-
-## Required pieces
-
-- Discover dependencies, mark changed units, and propagate that decision to
-  dependents until it settles. Handle cycles as groups. Do this before loading
-  IR that may be stale; newly discovered dependencies must also join the plan.
-- Record actual inputs. An object can own several source units, so track all
-  of their sources and the objects resolved through library search paths.
-  The current check assumes `buildDir/name.o`; a missing file has timestamp
-  zero and does not trigger rebuilding. Missing inputs must invalidate or
-  produce a useful error rather than silently accepting an old result.
-- Record compiler and serialization versions, target, ABI, and relevant
-  options. Content hashes would also detect changes with preserved timestamps.
-  Specify which changes require rebuilding source and which reject an
-  incompatible source-free library.
-- Make build targets match output ownership. The old ignored `testModule0`
-  expects separate A.o and A/B.o, while the current compiler can bundle several
-  units into one object. The target must identify the complete set it owns.
-- Provide an "ensure current" build operation. Explicit source compilation
-  currently always recompiles. An unchanged build should do no compilation or
-  linking; a changed object or link input should trigger relinking.
-- Publish successful outputs without leaving a partial object accepted after
-  failure, and keep the recorded inputs consistent with those outputs.
-
-Initially, rebuilding every dependent of a changed object is a reasonable
-conservative rule. Fine-grained interface/body fingerprints can come later.
-
-## Suggested first implementation
-
-Put a small build driver around the compiler with explicit object targets,
-recorded inputs, and dependency propagation. Keep individual compilation
-requests straightforward. A clean build and an incremental build must produce
-the same observable program behavior.
-
-Cover unchanged builds, direct and transitive source edits, inlined constants
-and bodies, cyclic dependencies, bundled sources, removed inputs, library-path
-changes, compiler/target changes, and failed builds. Use controlled timestamps
-or hashes instead of sleeps. Replace the ignored historical experiment with
-tests matching the chosen object ownership model.
-
-Selective library IR loading is separate future work. It can reduce compile
-cost, but is not required to make conservative incremental rebuilding correct.