[codex] Fix duplicate timeline placeholder cards

[utopiafar]

Summary

• Fixes [Bug]输入新卡片时，主页信息流上会短暂出现两个占位卡片 #143 by making the in-memory timeline list idempotent by TimelineCardModel.id.
• Upserts locally submitted/card-added cards instead of blindly inserting duplicates.
• Collapses duplicate processing copies when card updates arrive, while keeping unloaded filtered-list cards hidden.
• Adds a stable key to timeline entries and focused unit/widget coverage for duplicate submission, update, and pagination overlap cases.

Root Cause

A newly submitted card can enter the TimelineViewModel from more than one local UI/update path while it is still in processing state. addCard() always inserted at index 0, so two copies of the same fact id could be visible until a later refresh or completed card update rebuilt the list from storage.

Validation

• dart pub get --offline --no-example
• flutter test --no-pub test/ui/timeline
• dart analyze lib/ui/timeline/view_models/timeline_viewmodel.dart lib/ui/timeline/widgets/timeline_screen.dart test/ui/timeline/view_models/timeline_viewmodel_test.dart test/ui/timeline/widgets/timeline_entry_dedupe_test.dart (passes with existing info-level timeline_screen.dart warnings for deprecated withOpacity and one existing async-context lint)
• git diff --cached --check

[github-actions]

PR Preflight Summary / PR 预检汇总

中文

• 统一结论：低风险：两个预检均已完成，质量预检通过，可走普通手动合并流程。
• Policy preflight：低风险。未命中打回、高风险或警告规则。
• Flutter quality：通过。Analyzer 和 test baseline 均未发现新增问题。
• PR head：5dc5b0be35311d44e88b1688fb5440ed32709148
• Policy run：26040202577
• Flutter run：26040202619

English

• Combined result: Low risk: both preflights completed and quality passed; use the normal manual merge flow.
• Policy preflight: LOW RISK. No blocking, high-risk, or warning policy signal was found.
• Flutter quality: PASS. Analyzer and test baselines found no newly introduced issue.
• PR head: 5dc5b0be35311d44e88b1688fb5440ed32709148
• Policy run: 26040202577
• Flutter run: 26040202619

PR Policy Preflight / PR 规则预检

PR Policy Preflight / PR 规则预检

中文

• 判定：低风险
• 变更文件数：0
• 变更行数：0
• Diff 是否截断：false

未发现确定性规则问题。

English

• Decision: LOW RISK
• Changed files: 0
• Changed lines: 0
• Diff truncated: false

No deterministic policy findings.

PR Flutter Quality / Flutter 质量预检

PR Flutter Quality / Flutter 质量预检

中文

• 总体：通过
• Analyzer baseline：通过
• Test baseline：通过

English

• Overall: PASS
• Analyzer baseline: PASS
• Test baseline: PASS

Flutter Analyzer Baseline

• Base issues: 328
• PR issues: 328
• New issues: 0

No new analyzer issues introduced by this PR.

Flutter Test Baseline

• Base failures: 0
• PR failures: 0
• New failures: 0

No new Flutter test failures introduced by this PR.