Re-pin vendored Interchange to the workflow.json retirement

[TheGreatAxios]

Re-pins the vendored Interchange trees from 59f5e7b9 to upstream main
tip 4ed8baf4 (45 commits), whose headline change is the retirement of the
on-disk workflow.json. CL-6324.

What this lands

• All 21 vendor/intx/* rows re-copied at 4ed8baf4. Nine trees
  actually changed (hub-sessions, workflow-host, workflow,
  workflow-deploy, types, hub-api, db, agent, hub-agent); the
  rest are byte-identical at both commits and were re-pinned so the ledger
  records one commit rather than a mix — which also collapses
  inference-catalog's separate 5d2aa94a pin.
• Every workbench-local delta re-applied. Upstream subsumed none of
  them, and none of the five files they touch changed upstream across the 45
  commits, so all four re-applied without conflict: the inference.usage
  forward, the terminal-anchor ownsWorkflowRunRepo gate, the
  hasConversationText mail drop, and the needs-you approval-route
  carve-out. Their tests pass (11 tests, 3 files).
• VENDORED.md, each VENDORED-FROM, and the kill-date tree hashes
  updated together; check:killdates is green.
• One app-side conversion: the folded launch builds its single-step
  agent through buildSingleStepAgentDefinition directly, now that the
  wrapHarnessAsSingleStepWorkflow adapter over it is gone.

What this does NOT land, and why

The app-side conversion is not here. Upstream retired the live-authored and
instance deploy chains outright — deploySingleStepAtHead,
deployInstanceAtHead, createWorkflowDeployOrchestrator, the deploy
frame's definition field, and the deploy-ref child spawners. Source-ref is
the only deploy lineage left: a definition is evaluated from the
deployment's own source closure and re-verified in-child.

Workbench has no code-sourced deploy front. Every run it launches goes
through packages/folded-runs' deployAtHead, which synthesizes a
single-step definition in memory and hands it to the deleted
deploySingleStepAtHead. The replacement takes a registry name@range pin
or an asset tarball and resolves a closure from it, so converting means
giving a folded run a real source package — a migration in its own right,
well past this change's box.

The trees are not separable along that line: hub-sessions (deploy
front), workflow-deploy (orchestrator), types (deploy frame),
workflow-host (child definition load), db (frozen approval bundle,
migrations 0082/0083) and hub-api (run trigger) move together, and
apps/sidecar reads the frame both sides write. Leaving any one on the old
pin splits the frame contract down the middle. So the branch re-pins all of
them and carries the conversion as known, mapped work.

apps/sidecar's ledger row deliberately stays at 59f5e7b9: the fork has
not been reconciled with upstream's own conversion of the same files.

docs/revendor-inventory.md carries the full map — the four open conversion
sites, and the upstream files that are the reference implementation for each.

State of the build

Red, expected, on two counts:

1. Typecheck fails at the conversion sites above — folded-runs
   (deploySingleStepAtHead), apps/sidecar
   (createWorkflowSpawnChild/createWorkflowSpawnSuspendableChild,
   projection.definition, SpawnTimeEnv.referencedDefinitionHashes,
   RunWorkflowChildBindings.workflowDefinitionRepoId), and the packages
   that typecheck through folded-runs. Every failure is one of those
   contract changes; none is incidental.
2. The branch is cut from cl-5879-shell-mock-v2, not post-merge main,
   and needs a rebase once PR CL-5879: Shell Mock v2 — two-column workbench product surfaces #52 lands.

Lint and formatting are clean, and the vendored delta tests pass.

Draft until the deploy-front conversion has an owner and a plan.

[TheGreatAxios]

Superseded: the re-pin landed via the conversion stack (PR #108, merge fbf0852) — all 21 vendored rows at 4ed8baf4 with every local delta re-applied. See CL-6324.