v2026.7.21: SPEC-236 Phase D v0.1 — Local Pipeline Graph

Phase D starts where CapTP gets interesting: an unresolved result is a reference you can name in later work. Full multi-hop wire envelopes are not here yet. What is here is the local substrate those envelopes will sit on: dependency edges, failure cascade, and honest sequential downgrade.

What’s new

`pipeline_link`

let root: Promise[u64] = promise.new[u64]()
let seg: Promise[u64] = promise.new[u64]()
_ = promise.pipeline_link[u64, u64](root, seg)
// pipeline_dependent_count(root) == 1

The child is a pipeline segment of the parent ([PROM:5.1]). It does not auto-resolve when the parent succeeds — the next producer still owns that resolve. It does fail if the parent breaks.

UpstreamFailed cascade ([PROM:5.3])

If the root fails, is cancelled, or is destroyed while still pending, every pending dependent (and their dependents) transitions to Failed(ERR_UPSTREAM_FAILED).

_ = promise.pipeline_link[u64, u64](p0, p1)
_ = promise.pipeline_link[u64, u64](p1, p2)
_ = promise.signal_fail[u64](promise.resolver[u64](p0), promise.ERR_SCHEMA_MISMATCH)
// p1 and p2 → STATE_FAILED, failure_kind == ERR_UPSTREAM_FAILED

Tombstone / replay token ([PROM:5.3.3])

_ = promise.set_tombstone_token[u64](p0, 0xC0FFEE01 as u64)
// after cascade, dependents carry the same token via tombstone_token()

Sequential vs envelope mode ([PROM:5.2.3])

Mode	Meaning
`PIPELINE_MODE_SEQUENTIAL` (default)	Segments recorded; driver awaits then issues next call
`PIPELINE_MODE_ENVELOPE` (reserved)	True multi-segment wire not live yet

If you set ENVELOPE today, pipeline_link still records the segment and increments pipeline_downgrade_count() so nothing is silently dropped. That counter is the runtime evidence behind P236-W001.

API surface

API	Role
`pipeline_link[T,U](parent, child)`	Record segment
`pipeline_dependent_count[T](parent)`	Direct child count
`set_tombstone_token` / `tombstone_token`	Failure record token
`pipeline_mode` / `pipeline_set_mode`	Capability mode
`pipeline_downgrade_count`	Sequential fallback observations

Verification

./scripts/zb test-cluster-promise-pipeline-cascade
./scripts/zb test-cluster-promise-pipeline-downgrade

Scope and what’s next

SPEC-236 phase	Status
A — local Promise slots	✅
B — `.call()` sugar	✅
C — SBI PromiseId	✅
D v0.1 — local pipeline graph	✅ (this release)
D.1 — wire envelopes + `Promise.call`	Next

Reference

std.cluster reference
Phase C
Monastery: Pipeline Cascades (08-promise-pipeline-cascade.md)