bd mol pour: formula gate steps fail with 'invalid issue type: gate' — missed IsValidWithCustom call site

[pstradowski]

Bug

bd mol pour fails when a formula step has gate = { type = "human" }:

Error: pouring proto: failed to create issue from meow-openspec.gate-proposal-review: validation failed for issue : invalid issue type: gate

The formula-pour code path creates a companion bead of type gate, but the validation uses IsValid() (built-in types only) instead of IsValidWithCustom().

Workaround: bd config set types.custom '["gate"]' — registers gate as a custom type.

Reproduction

# .beads/formulas/repro.formula.toml
formula = "repro"
phase = "liquid"

[[steps]]
id = "work"
title = "Do work"
type = "task"

[[steps]]
id = "review"
title = "Human review"
type = "task"
depends_on = ["work"]
gate = { type = "human" }

bd init   # if not already initialized
bd formula list   # should show "repro"
bd mol pour repro
# Error: pouring proto: failed to create issue from repro.gate-review: validation failed for issue : invalid issue type: gate

Diagnosis

This is the same class of bug as #3030 (bd update --type rejects custom types). That issue identified IsValid() vs IsValidWithCustom() as the root cause and was fixed in #3159 for three call sites in the update path.

The formula-pour code path is a fourth call site that was missed by the #3030 fix. The pour pipeline creates companion beads of type gate when a formula step has a gate field, but the creation goes through a validation path that still uses IsValid().

Supporting evidence: the types.custom example in #3030 already includes gate in its list, confirming that bd's own ecosystem expects gate-type beads to exist.

Expected behavior

bd mol pour should succeed when a formula has gate steps, without requiring the operator to manually register gate as a custom type. Either:

1. The formula-pour validation should use IsValidWithCustom() (same fix as bd update --type rejects custom types (agent, convoy, etc.) #3030), or
2. bd mol pour should auto-register gate as a custom type when it encounters formula gate steps, or
3. Gate companion beads should use type task instead of gate (with gate semantics carried in metadata/labels).

Environment

• bd version: 1.0.0 (Homebrew, macOS)
• Formula schema: TOML with gate = { type = "human" } on steps
• Storage: embedded Dolt mode

I'm happy to submit a PR if you confirm the diagnosis and preferred fix approach.