Refactor MIR field/index access to projection places

[itsfuad]

Goal

Keep storage projection separate from value access across fields, indexes, dereferences, slices, and future maps.

Current Projection Model

• Reads use explicit Load(place).
• Writes use generic Store(place, value).
• Field storage uses ProjectField.
• Array and dynamic-array element storage uses ProjectIndex.
• Address-taking and receiver borrows reuse place projection instead of copying values into temporaries.

Progress

• PR Add MIR field projections #34 replaced tactical field address/store nodes with ProjectField, Load, and Store.
• PR Implement array slice value semantics #42 added builtin index assignment through ProjectIndex.
• PR Implement dynamic array and reference semantics #44 adds bounds-checked dynamic-array reads/stores through the same ProjectIndex path and preserves nested selector receiver borrows from original storage.

Hard Line

Do not add one-off address nodes such as IndexAddr, SliceAddr, or MapAddr. New composite access must extend projection/place architecture.

Remaining Acceptance Criteria

• Decide whether MIR keeps individual projection nodes or grows a first-class Place model.
• Add dereference and slice projections needed by safe slice-view creation/lowering.
• Define map element addressability before map lowering.
• Keep backend GEP/load/store logic shared across composite access kinds.
• Add tests for deeper mixed projection chains and mutation across control flow.

Related

• Implement array and slice value semantics #27 tracks remaining dynamic-array and slice-view operations.
• Track reference origins and borrow conflicts #43 tracks reference origins and borrow conflicts layered on projected places.

[itsfuad]

PR #44 merged into main at merge commit 80b8ae9. Dynamic-array reads and stores now use bounds-checked ProjectIndex plus shared Load / Store; nested reference receiver borrows preserve original projected storage. Issue remains open for first-class place direction, slice/deref projections, map addressability, and deeper mixed projection coverage.