feat(layout/render): I-paged inline fragment tree — per-page slice + continuation rebase (slice 4 / I-paged)

[send]

Slice 4 / I-paged — inline fragment tree, first installment

The render↔layout inline-pipeline convergence's last structural gate was frag_constraint.is_some() routing paged/multicol inline to the legacy single-linear-pass path. This is the I-paged installment of slice 4: the inline portion of a Z-ready fragment tree, scoped to paged fragmentation (multicol = I-multicol, a separate slice; bidi/justify/text-transform remain independent slices; legacy deletion is terminal).

Plan-memo: render-layout-inline-convergence-slice4-fragtree-plan (/elidex-plan-review GREEN, 2-round). Master: render-layout-inline-convergence-plan §6 slice 4.

What changed

• InlineFlow → { fragments: Vec<InlineFragment> } (InlineFragment { generation, lines }) — the inline node of the project's fragment tree. A 1-entity→N-fragment relation fits an ECS component, unlike the N:M entity↔layer relation that forces the layer tree into a standalone structure (design §15.4.1). Non-fragmented runs keep a single generation-0 fragment.
• Paged-scoped persist gate (F3) — fragmentation_type (Page/Column) threaded into InlineFragConstraint at both construction sites; the gate drops frag_constraint.is_none() for Page runs only. Multicol (Column) stays gated to legacy (its accumulate + column shift + balanced-fill probe-gating are I-multicol).
• Single-source slice + continuation rebase (F2) — new LinePacker::slice_and_rebase_fragment: every block coordinate the packer records (flow lines, entity rects → LayoutBox/InlineClientRects, abspos static positions, positioned-atomic placements) is a snapshot of the same current_block_offset, so the slice to [skip_lines, effective_line_count) and the rebase to the fragmentainer block-start are applied once, before the content_origin fold — no cross-consumer desync.
• Render consume — the consume gate + emit_inline_flow iterate fragments filtered by page generation (shared fragment_matches_page predicate keeps them in sync, D4).

Why

Paged multi-line inline was broken on both the (gated-off) persisted path and the box path (continuation geometry was never rebased — the founding gate test said so). This makes a page-spanning paragraph render correctly per fragment: continuation fragments rebased to the page content top, the tail dropped after an orphans/widows break.

Tests

6 new (5 layout + 1 render): paged-persists / multicol-still-gated / continuation-rebase / tail-drop-after-break / clientRects==flow-lines single-source / render-generation-filter. All changed-crate tests + full mise run ci (3-OS check + clippy + nextest + doc-tests + deny) green.

Gate

Full 6-stage pre-push: cargo fmt → mise run ci (green) → /code-review (high; 0 real bugs) → /simplify (single-pass union + shared predicate) → /review → /elidex-review (5-axis: 0 CRIT, fixed 1 IMP §15.4.1 citation + 1 IMP test-comment; 1 MIN inline/mod.rs 1103-line growth deferred consistent with prior slices). Cap-neutral (convergence/correctness refactor, no new #11-* slot).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Implements the slice 4 / I-paged portion of the render↔layout inline convergence by introducing an inline fragment-tree representation (InlineFlow → fragments: Vec<InlineFragment>) and enabling paged fragmentation to persist/consume per-page inline geometry via a single-source slice + continuation rebase pass.

Changes:

• Introduces InlineFragment { generation, lines } and updates InlineFlow to carry per-fragment line sets (common case remains a single fragment via InlineFlow::single).
• Adds LinePacker::slice_and_rebase_fragment(skip_lines, effective_line_count) and wires it into inline layout for paged fragmentation only (multicol/Column remains gated).
• Updates render consumption to filter persisted fragments by page generation (shared fragment_matches_page predicate) and updates/extends tests accordingly.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/layout/elidex-layout-block/src/inline/pack.rs	Adds single-pass geometry slicing + continuation rebase for paged fragments.
crates/layout/elidex-layout-block/src/inline/mod.rs	Threads fragmentation type into the gate and invokes slice+rebase for paged runs before consumers.
crates/core/elidex-ecs/src/components.rs	Changes InlineFlow to hold Vec<InlineFragment> and adds InlineFlow::single helper.
crates/core/elidex-render/src/builder/inline.rs	Consumes persisted inline flows per-page by filtering fragments by generation.
crates/core/elidex-render/src/builder/tests/inline_flow.rs	Updates existing tests to build InlineFlow::single and adds generation-filter consume test.
crates/layout/elidex-layout-block/src/inline/tests/inline_flow.rs	Updates tests for fragment-based flow and adds paged I-paged behavior tests (persist gate, rebase, tail drop, clientRects SSoT).
crates/layout/elidex-layout-block/src/inline/tests/relpos_subflow.rs	Updates flow inspection to read from fragments[0].lines.
crates/layout/elidex-layout-block/src/block/children/shift.rs	Shifts inline flow geometry across all fragments during subtree shifts.
crates/layout/elidex-layout-block/src/block/children/helpers.rs	Threads fragmentation_type into InlineFragConstraint construction.
crates/layout/elidex-layout-block/src/block/mod.rs	Threads fragmentation_type into inline fragmentation constraint for block layout.
crates/layout/elidex-layout-block/src/block/tests/margin_collapse.rs	Updates test fixture construction to use InlineFlow::single and fragments[0].
crates/layout/elidex-layout-block/src/block/tests/fragmentation_advanced.rs	Updates constraint construction to include fragmentation_type.
crates/core/elidex-ecs/src/lib.rs	Re-exports InlineFragment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[send]

@codex[agent]

[send]

@codex[agent] review

[send]

@codex[agent] review deep