[fix] workflow-related fork issues

[jp-agenta]

Description

POST /workflows/variants/fork silently returned {"count": 0} for any invalid/partial payload.

Made the trailing tip revision optional (fork now works when the user only supplies workflow_variant + a source ref), and converted the remaining misuses into a typed VariantForkError that the routers surface as HTTP 400 with a structured detail.

Same DAO backs workflows, applications, evaluators, and queries forks — all four endpoints are fixed by this change. Routers for workflows/applications/evaluators now translate VariantForkError → 400.

Cause

The shared fork_variant DAO is wrapped in @suppress_exceptions(), so the AttributeError raised when the caller omitted the optional revision / workflow_revision block was swallowed into None → empty response.

Fixes

• core/git/types.py — new module with GitError / VariantForkError.
• dbs/postgres/git/dao.py::fork_variant — validate inputs (missing variant, missing source ref, unresolved source revisions) with VariantForkError; guard the optional tip revision commit; @suppress_exceptions(exclude=[VariantForkError]).
• apis/fastapi/{workflows,applications,evaluators}/router.py — catch VariantForkError → HTTPException(400, detail=...).
• tests/pytest/acceptance/workflows/test_workflow_lineage.py — 4 new tests: fork without revision (succeeds, copies history), missing variant payload (400), missing source ref (400), unknown source (400).

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Project	Deployment	Actions	Updated (UTC)
agenta-documentation	Ready	Preview, Comment	Apr 22, 2026 0:27am

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Updated at 2026-04-22T12:29:10.403Z