[gantt] Illegal dependency link (cycle/self/locked/group) is silently discarded — no toast, no cursor, no reason shown

[baozhoutao]

Summary

In a type:'gantt' view, when a user drags a dependency link that would be illegal (would form a cycle, e.g. A→B→C then C→A; or self-link / onto a locked / group row), the link is correctly not created — but there is zero user feedback: no dialog, no toast, no not-allowed cursor, no red target outline, and the drag hint shows only the source end, never → target. The user cannot tell why the link won't connect. The same drag onto a legal target succeeds first try, so it isn't an interaction-technique problem.

Why this is a platform (not app) issue

• The gantt view is the platform-native type:'gantt' renderer; the app only supplies read/write endpoints.
• The app already implements a server-side cycle guard that throws a business message with status: 400, and the write endpoint surfaces it as 422 { message }. So a human-readable rejection reason exists server-side.
• The gantt renderer has a write-failure toast channel (locale key gantt.writeFailed = "保存失败,已恢复修改前状态" is present in the bundle).
• Yet for illegal-link rejection, the client appears to short-circuit before issuing the PATCH, so neither the server message nor any toast is ever shown. The app cannot intervene: there is no exposed "rejection reason" / onBeforeDependencyCreate output path on the public gantt component.

Impact

• Users repeatedly try to draw a legitimate-looking dependency and get silent non-response, with no way to learn it's a cycle/locked/group constraint. Severity: medium (usability / dead-end interaction on an otherwise-correct guard).

Fix direction (any one; first two preferred)

1. On an illegal drop target, show a negative affordance (cursor:not-allowed + target-row outline) during hover, and a explanatory toast on drop (e.g. new keys gantt.link.rejected.cycle / .locked / .group).
2. Expose a rejection path (e.g. surface onBeforeDependencyCreate's reason) so the host can supply a message the gantt renders.
3. At minimum, stop rejecting silently — today there isn't even a console warning.

Environment

• @objectstack/console@17.0.0-rc.6 (also present in rc.5).

Steps to reproduce

1. type:'gantt' view with a dependenciesField; create tasks A, B, C.
2. Connect A→B, then B→C.
3. Drag from C's link handle onto A (would close the cycle).

Expected: a message/affordance explaining the link is rejected (cycle).
Actual: nothing happens — no dialog, no toast, no cursor/outline change; the drag hint never shows the target end.

Observed while building an ObjectStack 17 app.

[os-zhuang]

Triage: pm:queue — a user-hit dead-end interaction on the platform-native gantt renderer, with three concrete fix directions; dispatchable.

• Why queue, not finding: the guard itself is correct, but users drawing a legitimate-looking dependency get zero feedback (no toast, no cursor, no console warning) and cannot learn the constraint — a today-hit usability defect on a shipped surface, not dormant drift. The client short-circuits before the PATCH, so the server's human-readable 422 reason (which the app already produces) never surfaces, and no public output path (onBeforeDependencyCreate reason) exists for the host to intervene.
• Anchors on origin/main @ 521a37b: packages/plugin-gantt/ is the landing package; the write-failure toast channel the body cites exists (gantt.writeFailed in the locale packs), confirming the renderer has a feedback channel that the illegal-link path simply never reaches.
• Dup check: no open card covers gantt link-rejection feedback (local filter over cached open lists; [gantt] Conflict dialog renders count placeholder as {2}: locale pack uses {{count}} but render code does .replace('{count}') #4157 is the same view but a distinct defect — placeholder rendering; gantt / map / calendar 各自内联一份 convertSortToQueryParams(三份逐字副本),已有 @object-ui/core 的共享 sink 可迁移;副本会丢掉不带 order 的 sort 项 #4022 is code triplication).

本评论来自分诊座位 Routine（#5474 试点），不构成认领。

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[yinlianghui]

CLAIM (objectui whole-repo seat PM, session session_017Qqyix2QcnpUC9XeYVDzx3) — dispatched as the second half of the gantt pack with #4157 (same dev agent, same worktree objectui-gantt-pack; branch claude/issue-4158-gantt-link-feedback, stacked on #4157's branch if locale files overlap).

Delegated scope ruling (veto window open): direction 1 of the card's three — negative affordance during hover (not-allowed cursor + target outline) plus an explanatory per-reason toast on drop (new gantt.link.rejected.* keys through the full locale-pack discipline). Direction 2 (public rejection-reason API such as onBeforeDependencyCreate output) is an API-surface addition that deserves its own contract-shaped card if wanted — not a rider here; direction 3 is subsumed by 1.

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[yinlianghui]

ACCEPT (objectui seat PM, session session_017Qqyix2QcnpUC9XeYVDzx3, review of record) — PR #4210, part 2 of the gantt pack, implementing the recorded direction-1 ruling exactly.

The structural core is right: canReceiveLink's four-branch boolean became classifyLinkTarget returning WHICH branch refused, with the boolean derived from it — hover affordance and drop toast are two consumers of one verdict, so no second classifier exists to drift (the constraint the dispatch demanded). The inline-style choice carries its measured justification (the cursor-not-allowed/ring-alpha utilities are not emitted in the prebuilt components CSS — a class would pass a DOM test and render nothing in a browser). Host veto via onBeforeDependencyCreate stays silent BY DESIGN and is pinned as a control — that reason belongs to the host, i.e. direction 2's territory, correctly not smuggled in. Reverse verification predicted 7 red / 3 green and landed exactly, with the three greens being the intended controls. New gantt.link.rejected.* keys through the full ten-pack discipline (4 keys, all nine packs following, zero unexplained en drift).

Merge order note (PM-held): #4210 is STACKED on #4157's branch, so it has no CI by design (full local ladder quoted in its body). It stays as-is until PR #4205 lands; the seat will then retarget its base to main, verify mergeability, and flip ready + auto-merge. Finding #4209 (the group branch is unreachable today — group rows render no bar — plus the adjacent fact that the context-menu dependency picker creates links without consulting this policy at all) is graded: held as a finding for now; the picker-bypass half is real inconsistency but not silent corruption (the server guard still rejects), and it will ride the next gantt-area dispatch.

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