PIR spawn prompt renders blank artifact filenames: {{artifact_name}} is not on TemplateContext and no spawn path supplies it

[waleedkadous]

Problem

codev-skeleton/protocols/pir/builder-prompt.md:33-35 consumes {{artifact_name}} in the phase list:

• plan phase: "write codev/plans/{{artifact_name}}.md"
• review phase: "write codev/reviews/{{artifact_name}}.md"

But artifact_name is not a field of TemplateContext (spawn-roles.ts:25-48) and no spawn path in spawn.ts supplies it. renderTemplate renders a missing key as an empty string, so every PIR builder's spawn prompt tells it to write codev/plans/.md and codev/reviews/.md. Verified 2026-07-29 against both files.

Only porch supplies artifact_name, for per-phase prompts — the spawn-time template never gets it.

Surfaced by the aspir-1273 builder during its phase-5 CMAP (correctly kept out of that project's scope: its contract is to match what spawn delivers, not to change another protocol's spawn behaviour).

Severity

Low-ish in practice: the blank renders in the spawn prompt's protocol overview, and porch's per-phase prompts later deliver the correct artifact name — so a PIR builder is misinformed at spawn but corrected per-phase. Still a real defect: the spawn prompt is the builder's first orientation, and "write codev/plans/.md" reads as broken.

Fix options (either is acceptable; second is recommended)

1. Supply it: add artifact_name?: string to TemplateContext and populate it in the issue-driven spawn path using the same derivation porch uses (issue number + slug). Keeps the concrete filename in the spawn prompt, at the cost of duplicating the derivation or extracting it to be shared.
2. Drop the placeholder (recommended): reword the two lines to defer to porch — e.g. "write the plan to codev/plans/ under the artifact name porch's phase prompt gives you." Zero code change, no derivation duplication, and consistent with the existing division of labour (porch owns per-phase artifact naming).

Whichever fix: mirror across codev/ and codev-skeleton/ if a local copy of the PIR protocol exists (currently skeleton-only), and grep both trees for other templates consuming {{artifact_name}} outside porch's per-phase delivery before claiming fixed.