Sync cost-lane roadmap authority with landed work

[gunbai-bot]

Summary

Correct the roadmap and design authorities so banked work is not redispatched: entry-graph-union slice 1 is recorded as merged and redirected to repeated-typecheck attribution; v1 run-stability M2 is recorded as landed with only its named follow-ups remaining; and the materialization kernel is re-homed as iteration-speed/runtime infrastructure with v1 exit as one consumer.

The plain planning docs preserve the superseded framing as correction history, while generated DESIGN.md and ROADMAP.md are refreshed from their .dag authorities.

Verification

• Verified Exclusive cost partition + selected-set closure overlap (Lane B slice 1, measurement only) #7483, v1-run-stability M2: Schedule-derived per-module retention #7129, On-success materialization receipt (#7499 blocker 6) #7505, Close the four review blockers on the merged run_stage extraction #7518, and WalkPlan schedule lens covers success-stage structure #7521 via gh pr view and local merge history.
• CTRL_BUILD_MODE=local ctrl-build -- cargo build --release --bin gunbc (pass; bounded retry at 4 jobs after host process pressure).
• target/release/gunbc run --source-root "$PWD/dag" --source-root "$PWD/src/v2" --entry dag/tools/generated_artifact_gate.dag --function main_wet (pass; regenerated committed projections).
• Focused roadmap completeness, v1-exit fan-in, and generated-artifact fixed-point witnesses each evaluated to true.
• git diff --check (pass).
• Pre-push cargo fmt --all --check (pass).

Impact

Docs and .dag authority only; no compiler or runtime implementation changes.