Allow artifact Q&A during and after implementation, including on PRs

[eshulman2]

Problem

Forge supports ? / @forge ask questions while generated artifacts are waiting at PRD, specification, plan, or task approval gates. Once implementation begins, that Q&A path is no longer generally available.

In particular, comments on the implementation GitHub PR currently recognize operational commands such as /forge skip-gate, /forge unskip-gate, and /forge rebase. Artifact questions on that PR are not routed to the Q&A handler. The existing GitHub Q&A handling is scoped to PRD/spec proposal PRs while their corresponding approval gates are active.

This prevents reviewers from asking questions such as:

• Why did the implementation choose this approach over the approved specification's alternative?
• Which PRD requirement is addressed by this change?
• How does this code relate to a particular task or design decision?
• What changed from the approved artifact during implementation?

Proposed behavior

Allow read-only artifact questioning throughout and after implementation, including from the implementation GitHub PR and after the workflow reaches a terminal state.

• Recognize ? ... and @forge ask ... on implementation PR comments.
• Continue supporting the same syntax on Jira.
• Resolve the relevant workflow by stable PR-to-ticket correlation.
• Answer using the approved PRD/specification/plans/tasks plus implementation context such as the PR diff, review state, and recorded workflow history.
• Reply in the channel where the question was asked.
• Do not treat a question as revision feedback, reopen completed work, change approval state, advance the graph, or trigger code changes.
• Record the Q&A in auditable history with artifact/revision references.

If required artifacts are unavailable or the question cannot be grounded in retained context, Forge should say so rather than inventing an answer.

Lifecycle and routing considerations

• Q&A must work at implementation, CI, human-review, merged/completed, and blocked stages.
• Terminal workflows currently ignore most resume events; read-only Q&A needs a path that does not resume or mutate the completed graph.
• Multi-repository workflows should route a PR question to the addressed repository work item while retaining parent-ticket artifact context.
• Bot-authored answers must not be reprocessed as new questions.

Acceptance criteria

• ? and @forge ask comments on an implementation PR receive an answer on that PR.
• The same artifact question works from Jira after implementation has started.
• Questions work after merge/workflow completion without reopening or advancing the workflow.
• Q&A does not alter approval, CI, review, retry, or completion state.
• Answers cite or clearly identify the artifact/version and implementation context used.
• Unknown or unavailable context produces a transparent “cannot determine” response.
• Tests cover implementation, CI/review, terminal, blocked, duplicate/replayed, and bot-comment cases.