Rewrite plan.md to reconcile the original "SpecForge Redesign Plan" (from-scratch,
torchrun-native, HTTP-only) with the landed DataFlow runtime/ spine. Docs only — no
code change.

- Canonical substrate = runtime control + data plane (SampleRef + FeatureStore incl.
  Mooncake + FeatureDataLoader). The isolated-pool / >100GB/s requirement overturns the
  original "no Mooncake" bet.
- No separate HiddenStateStream source of truth — FeatureDataLoader over
  SampleRef+FeatureStore IS the stream; topology variation lives in (ref source +
  FeatureStore), shielded from training.
- training/inference become plan.md-style domain packages on top: keep the runtime
  TrainerCore/DraftTrainStrategy seam, add Trainer lifecycle + managers (checkpoint/
  eval/no_sync/resume); converge SGLangAdapter -> TargetEngine + backends.
- colocated lightweight path = control plane opt-in/no-op, guarded by a
  colocated == disaggregated numerical-equivalence gate.
- original redesign draft preserved verbatim in docs/redesign-draft-legacy.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Add docs/roadmap/ — per-phase Goal/Target/Implementation/Tests/Done-when
across three tracks (domain-refactor, online-disaggregation, eval-and-breadth)
plus a README index. The online track folds in the former online-disaggregation
roadmap (#618) so there is one roadmap home.

Apply two scope decisions to plan.md and the roadmap:
- Frozen target, no weight sync. "Train-with-decode" = a frozen target streaming
  hidden states (W2/W3), not a serve-and-push workload. Drop the W4 weight
  lifecycle (WeightVersion/WeightPublisher/update_draft_weights/ServingTrafficStream);
  draft_weight_version is provenance only.
- Ray is an open decision, not a non-goal. Candidate for the O2 scale-out
  orchestrator; decision gate in the online roadmap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

… W3′ naming

Review fixes (verified against the files):
- Status (confirmed): stop calling the in-review composable-launch stack (#627/#628/#629)
  "landed"/"DONE"/"done". Split the genuinely-merged spine from the in-review stack in §1; one
  consistent "in review" label in §1/Phase A/success table and across the roadmap (README, Phase A).
  Leave the spine's "landed" wording (it is merged).
- Module placement (confirmed): Evaluator/EvalCache are top-level domain managers
  (specforge/eval/), not specforge/runtime/eval/ — fix the eval-and-breadth.md outlier to match
  plan.md §2.3 and domain-refactor.md.
- W3′ naming (confirmed): SGLangServerEngine is ONE engine with two feature transports
  (capture-into-FeatureStore for W3/O1.3, inline-HTTP for the light W3′) — disambiguate in §2.2,
  the workload table and §G2 rather than overloading one name.
- O1.3 spike (reviewer's premise refuted — it is already an explicit 🔴 gate): added the valid
  narrow point instead — the spike scopes only the sglang_server slice of Phase B; the de-EAGLE3
  extraction and domain Trainer carry no engine risk.

Additional contradictions found by a completeness sweep and fixed:
- StrategySpec registry: plan.md said it "stays in runtime/training unchanged" but §6 + Phase E
  move it — clarify the per-step strategy seam stays, the registry converges into training/strategies/.
- TargetEngine source: extracted from modeling/target/*TargetModel (adapters wrap it), not
  "absorbs runtime/inference adapters".
- Draft package: models/drafts is the target layout; note today's modeling/draft/ + real filenames.
- Dependency graph: align domain-refactor (E depended on {C,D}) with README (D→E, C parallel).
- Drop the up-19/up-20 branch tags that only appeared in the online doc.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>