Implement ROADMAP.md Phases 0-3: CI and test coverage gaps

.github/workflows/ci.yml

@@ -117,6 +117,30 @@ jobs:
       - name: Test (stde)
         run: cargo test --features stde
 
+      - name: Build (bytecode,taylor)
+        run: cargo build --features bytecode,taylor
+
+      - name: Test (bytecode,taylor)
+        run: cargo test --features bytecode,taylor
+
+      - name: Build (bytecode,stde)
+        run: cargo build --features bytecode,stde
+
+      - name: Test (bytecode,stde)
+        run: cargo test --features bytecode,stde
+
+      - name: Build (taylor,stde)
+        run: cargo build --features taylor,stde
+
+      - name: Test (taylor,stde)
+        run: cargo test --features taylor,stde
+
+      - name: Build (bytecode,taylor,stde)
+        run: cargo build --features bytecode,taylor,stde
+
+      - name: Test (bytecode,taylor,stde)
+        run: cargo test --features bytecode,taylor,stde
+
   coverage:
     name: Coverage
     runs-on: blacksmith-2vcpu-ubuntu-2404

CLEANUP_PLAN.md

@@ -2,6 +2,8 @@
 
 **Generated**: 2026-03-13 | **Project**: echidna v0.4.0 | **LOC**: ~23,400 source, ~15,700 tests
 
+> **Status (2026-03-14)**: Phases 0–3 are complete. All safety comments, lint suppression comments, CI gaps, documentation fixes, and test coverage gaps have been addressed. Remaining work is in Phases 4+ (deferred features and aspirational improvements). See ROADMAP.md for the current state.
+
 ## Executive Summary
 
 Three specialist agents (Infrastructure, Design, Documentation) reviewed the echidna codebase. The project is in strong shape — zero lint errors, zero dead code, zero debug artifacts, clean architecture with correct dependency direction, and comprehensive test coverage across 37 integration test files.

ROADMAP.md

@@ -0,0 +1,138 @@
+# Roadmap
+
+**Version**: v0.4.1+ | **Last updated**: 2026-03-14
+
+All core roadmap items (R1–R13) are complete. This document captures forward-looking work: cleanup backlog, infrastructure gaps, deferred features, and aspirational improvements.
+
+For the historical implementation log, see [docs/roadmap.md](docs/roadmap.md). For deferred/rejected rationale, see [docs/adr-deferred-work.md](docs/adr-deferred-work.md).
+
+---
+
+## Phase 0: Foundation ✅
+
+Safety and compliance items with no dependencies. **Complete** (v0.4.1).
+
+| # | Item | Status |
+|---|------|--------|
+| 0.1 | Add SAFETY comments to 13 unsafe blocks | ✅ Done |
+| 0.2 | Add explanatory comments to 8 `#[allow]` suppressions | ✅ Done |
+
+---
+
+## Phase 1: Cleanup ✅
+
+Code duplication consolidation. **Complete** — all items were already addressed in v0.4.1 codebase review.
+
+| # | Item | Status |
+|---|------|--------|
+| 1.1 | Consolidate `greedy_coloring` → delegate to `greedy_distance1_coloring` | ✅ Already delegates |
+| 1.2 | Consolidate `sparse_hessian` → call `sparse_hessian_with_pattern` | ✅ Already a wrapper |
+| 1.3 | Extract shared opcode dispatch from `forward`/`forward_into` | ✅ Uses `forward_dispatch` helper |
+| 1.4 | Consolidate `column_coloring`/`row_coloring` → generic helper | ✅ Delegates to `intersection_graph_coloring` |
+| 1.5 | Extract helper from `GpuTapeData::from_tape`/`from_tape_f64_lossy` | ✅ Shares `build_from_tape` |
+
+---
+
+## Phase 2: Infrastructure ✅
+
+CI and workflow gaps. **Complete**.
+
+| # | Item | Status |
+|---|------|--------|
+| 2.1 | Add `diffop` feature to CI test and lint jobs | ✅ Done (v0.4.1) |
+| 2.2 | Add `parallel` feature to `publish.yml` pre-publish validation | ✅ Done (v0.4.1) |
+| 2.3 | Expand MSRV job to test key feature combinations | ✅ Done — tests bytecode, taylor, stde, and all pairwise/triple combos |
+
+---
+
+## Phase 3: Quality ✅
+
+Documentation fixes and test coverage gaps. **Complete**.
+
+### Documentation
+
+| # | Item | Status |
+|---|------|--------|
+| 3.1 | Update CONTRIBUTING.md architecture tree | ✅ Done (v0.4.1) |
+| 3.2 | Fix algorithms.md opcode count | ✅ Done (v0.4.1) |
+| 3.3 | Move nalgebra entry to Done in ADR | ✅ Done (v0.4.1) |
+| 3.4 | Update roadmap.md stale `bytecode_tape` paths | ✅ Done (v0.4.1) |
+
+### Test Coverage
+
+| # | Item | Status |
+|---|------|--------|
+| 3.5 | Add `echidna-optim` solver convergence edge-case tests | ✅ Done — near-singular Hessian, 1e6:1 conditioning, saddle avoidance |
+| 3.6 | Add `cross_country` full-tape integration test | ✅ Already has 5+ cross-validation tests |
+| 3.7 | Add CSE edge-case tests | ✅ Done — deep chains, powi dedup, multi-output preservation |
+| 3.8 | Sparse Jacobian reverse-mode auto-selection test | ✅ Done — wide-input map forces reverse path |
+
+---
+
+## Phase 4: Deferred Features
+
+Valuable features without current demand. Revisit when a concrete use case arises.
+
+| # | Item | Effort | Revisit when | Source |
+|---|------|--------|--------------|--------|
+| 4.1 | Indefinite dense STDE (eigendecomposition for indefinite C matrices) | medium | A user needs indefinite C support | [ADR](docs/adr-deferred-work.md) |
+| 4.2 | General-K GPU Taylor kernels (beyond K=3) | medium | Need for GPU-accelerated 3rd+ order derivatives | [ADR](docs/adr-deferred-work.md) |
+| 4.3 | Chunked GPU Taylor dispatch (exceed 128 MB WebGPU limit) | small | Users hit the buffer limit in practice | [ADR](docs/adr-deferred-work.md) |
+| 4.4 | CUDA `laplacian_with_control_gpu_cuda` | small | CUDA users need variance-reduced Laplacian | [ADR](docs/adr-deferred-work.md) |
+| 4.5 | `taylor_forward_2nd_batch` in `GpuBackend` trait | small | Multiple backends need to be used generically | [ADR](docs/adr-deferred-work.md) |
+
+---
+
+## Phase 5: Aspirational
+
+Nice-to-haves with no urgency. Pursue opportunistically or if the relevant area is being actively modified.
+
+| # | Item | Effort | Impact |
+|---|------|--------|--------|
+| 5.1 | Decompose `stde.rs` (1409 lines) into sub-modules | medium | medium |
+| 5.2 | Add `#![warn(missing_docs)]` and fill gaps | large | medium |
+| 5.3 | Bulk-add `#[must_use]` to pure functions (~267 sites) | medium | low |
+| 5.4 | Audit `usize` to `u32` casts in GPU paths | small | medium |
+
+**Caution**: 5.1 risks breaking delicate Taylor jet propagation logic — only pursue if `stde.rs` continues to grow. 5.2 is large (all public items need docs) — consider enabling per-module incrementally.
+
+---
+
+## Blocked
+
+| Item | Blocker | Action |
+|------|---------|--------|
+| RUSTSEC-2024-0436 (paste via simba) — unmaintained | Upstream simba must release with paste alternative | Already ignored in `deny.toml`. Monitor simba releases. |
+
+---
+
+## Dependency Bump
+
+| Item | Current | Latest | Effort | Notes |
+|------|---------|--------|--------|-------|
+| cudarc | 0.17 | 0.19 | medium | Breaking API changes in 0.18. Defer until GPU backend is actively developed. |
+
+---
+
+## Rejected
+
+These items were evaluated and explicitly rejected. Rationale is in [docs/adr-deferred-work.md](docs/adr-deferred-work.md).
+
+- **Constant deduplication** — `FloatBits` orphan rule blocks impl; CSE handles the common case
+- **Cross-checkpoint DCE** — contradicts segment isolation design
+- **SIMD vectorization** — bottleneck is opcode dispatch, not FP throughput
+- **no_std / embedded** — requires ground-up rewrite (heap allocation, thread-local tapes)
+- **Source transformation / proc-macro AD** — orthogonal approach, separate project
+- **Preaccumulation** — superseded by cross-country Markowitz elimination
+- **Trait impl macros for num_traits** — hurts error messages, IDE support, debuggability
+- **DiffOperator trait abstraction** — `Estimator` trait already provides needed abstraction
+
+---
+
+## Dependencies Between Phases
+
+```
+Phase 0–3  (complete)        — all done as of 2026-03-14
+Phase 4  (deferred features)  — each item independent; all require active use of base feature
+Phase 5  (aspirational)       — independent nice-to-haves
+```