roadmap: Stage 5 full launch (IPC + Chapel + Tier-4) — OWNER-GATED meta-tracker

[hyperpolymath]

Origin

docs/ROADMAP.md §4 ("Current sprint — the smallest set that flips half the table") closing lines:

After S1–S5 land, the roadmap's next sprint takes up Stage 5 (IPC + Chapel + Tier-4 CI) and Stage 8 begins in parallel.

And the Stage-5 row in the 8-stage map:

Stage 5  Distributed & fast                 scale + specialised hardware
    5a  Cap'n Proto IPC                     Rust ↔ Julia, :8090
    5b  Chapel full integration             dispatch.rs picks by config
    5c  coprocessor abstraction             trait + tensor/vector/QPU/FPGA
    5d  Tier-4 live-CI provisioning         19 backends, Containerfile path

Scope (meta-tracker for the Stage 5 launch wave)

This is the umbrella tracker for the Stage 5 "next sprint" after S1-S5. The four constituent rows are tracked separately or already partially landed:

• 5a Cap'n Proto IPC — tracker roadmap: Cap'n Proto IPC schema finalisation (Stage 5a — OWNER-GATED, needs Opus sign-off) #194 (OWNER-GATED on Opus schema sign-off)
• 5b Chapel full integration — partially landed (L2.1 + L2.2 in main; L2.3+ gated on 5a per L1 Cap'n Proto dependency); cancel-token preemption tracked in the L2.3 issue (companion file)
• 5c Coprocessor abstraction — not yet trackered; trait + tensor/vector/QPU/FPGA pluggable backends
• 5d Tier-4 live-CI provisioning — 19 backends to provision via Containerfile path; references Containerfile.full (issue Containerfile.full claims "all tier 1-4 provers" but ships only Z3/Agda/Lean/Metamath #11 closed-already on Tier-1-4 claim drift)

OWNER-GATED — Opus must sign off on:

1. Cap'n Proto schema (5a precondition)
2. Coprocessor abstraction trait shape (5c precondition)
3. Tier-4 Containerfile budget for runner CI minutes (5d precondition)

Dependencies

• S1-S5 (sprint commitments) — all currently shown as ✓ done in ROADMAP §4 except S2 (hardware step still pending)
• roadmap: Cap'n Proto IPC schema finalisation (Stage 5a — OWNER-GATED, needs Opus sign-off) #194 Cap'n Proto IPC schema (5a, OWNER-GATED)
• Companion L2.3 cancel-token tracker (5b L2.3, GATED on 5a)
• No upstream blocker beyond the Opus-side design

Why filed

To make the cross-cutting "Stage 5 launch" commitment trackable as a single coordination point. Today the phrase "the roadmap's next sprint takes up Stage 5" lives only as a single sentence; this gives the four rows a place to coordinate completion and lets the owner mark the wave done when 5a + 5b + 5c + 5d all close.