[DanielNetzer]

Implements issue #293.

Molecule: mol-293-81411423ea633237194be568
Formula: forgecell-github-issue
Base: 33dfa8f3530aae2057b668a6295be2ec2d2dd6aa
Delivery: 3a3814f3481136bec76119c6b767deba90a4ef0d

Awaiting exact-commit CI and human review. Harness-reported checks are not independent CI evidence. No merge, deployment or issue closure is authorized.

[DanielNetzer]

Adversarial review (plugins slice 1b): no HIGH or MEDIUM findings, and no behaviour drift. I checked the argv, run options, the 7-call order, nil-runner fallbacks, error text, errors.Is behaviour, the import direction, and PRFields against prFields, which match character for character.

LOWs, for a later cleanup:

1. forge/github.go:153, delivery/publish.go:403: prFields is now defined twice, and the delivery copy is dead because every call site goes through forge. Nothing ties the two together, so a later edit to one would still pass the delivery characterization test. Fix: delete delivery's prFields.
2. forge/github_test.go:299-333: the failure matrix iterates over a map, so the subtest order varies. The outcome is still deterministic; this is cosmetic.
3. forge/github_test.go:249-257: assertGHOptions checks only known process.Options fields, so a field added later wouldn't be asserted.