kandev/docs/plans/mermaid-sequence-semicolon-rendering/task-03-deduplicate-task-diagram-toasts.md

id, title, status, wave, depends_on, plan, spec

id	title	status	wave	depends_on	plan	spec
03-deduplicate-task-diagram-toasts	Deduplicate task Mermaid error toasts	done	3	02-log-failed-diagram-source	plan.md	../../specs/ui/requirements/mermaid-rendering.md

Task 03: Deduplicate Task Mermaid Error Toasts

Acceptance

1. Chat and task-plan Mermaid failures share one in-memory task-ID registry and show at most one error toast per task during a frontend runtime, including after task-panel remounts.
2. A different task can show its own first toast, while non-task Mermaid failures retain the existing unsuppressed behavior.
3. Suppressed toasts do not suppress full console diagnostics, inline errors, debounce, successful-render recovery, or stale-render cancellation.

Verification

cd apps
pnpm install --frozen-lockfile
pnpm --filter @kandev/web test -- \
  components/shared/mermaid-block-streaming.test.tsx \
  components/shared/mermaid-error-toast.test.tsx
pnpm --filter @kandev/web exec eslint \
  components/shared/mermaid-block.tsx \
  components/shared/mermaid-block-streaming.test.tsx \
  components/shared/mermaid-error-toast.tsx \
  components/shared/mermaid-error-toast.test.tsx \
  --max-warnings 0

Files likely touched

• apps/web/components/shared/mermaid-error-toast.tsx
• apps/web/components/shared/mermaid-error-toast.test.tsx
• apps/web/components/shared/mermaid-block.tsx
• apps/web/components/shared/mermaid-block-streaming.test.tsx
• docs/plans/mermaid-sequence-semicolon-rendering/plan.md
• docs/plans/mermaid-sequence-semicolon-rendering/task-03-deduplicate-task-diagram-toasts.md

Dependencies

Task 02. Keep its full-source logging call ahead of toast suppression so every failed render remains diagnosable.

Parallelism

Sequential. This task builds on Task 02's chat rejection path and shares mermaid-block.tsx plus its streaming tests.

Inputs

• docs/specs/ui/requirements/mermaid-rendering.md
• docs/plans/mermaid-sequence-semicolon-rendering/plan.md
• apps/web/AGENTS.md
• .agents/skills/tdd/SKILL.md
• .agents/skills/mobile-parity/SKILL.md
• Existing deduplication patterns in apps/web/hooks/use-session-failure-toast.ts and apps/web/hooks/use-task-deleted-toast.ts.

Risks

• A hook-local Set does not survive task-panel remounts; keep the task history at module scope.
• Do not assign unscoped Mermaid errors to whatever task happens to be focused.
• Capture the task ID associated with the render/event so an asynchronous rejection cannot consume another task's allowance after focus changes.
• Reset module state explicitly in tests so cases remain isolated.

Output contract

Report RED/GREEN evidence, files changed, exact verification results, blockers or residual risks, and update this task plus plan.md to done.

Completion evidence

• RED: a MermaidBlock test lacked its required task state, demonstrating the new render path now captures task context before showing a toast.
• GREEN: pnpm --filter @kandev/web test -- components/shared/mermaid-block-streaming.test.tsx components/shared/mermaid-error-toast.test.tsx (8 tests).
• GREEN: the final focused suite passed 36 tests; changed-file ESLint passed with --max-warnings 0.