fix: allow multiple pipeline chunker nodes

[CaptainTimon]

What problem does this solve?

Closes #14772.

Pipeline workflows hid chunker nodes after one instance had already been added, which prevented users from adding multiple independently configured title/token chunking stages in the same pipeline.

What is changed?

• Keep only structural pipeline nodes (Parser, Tokenizer) restricted to a single canvas instance.
• Keep TokenChunker and TitleChunker available in the pipeline operator menu after one is already present.
• Align the pipeline singleton operator list with that behavior.

Behavior proof

• Before: PipelineAccordionOperators filtered TokenChunker and TitleChunker through restrictSingleOperatorOnCanvas, so the menu removed them once findNodeByName() found an existing node.
• After: the chunker menu always exposes [Operator.TokenChunker, Operator.TitleChunker], while Parser and Tokenizer still go through the singleton filter.
• The DSL builder already keys components by unique node ID, so multiple chunker nodes can keep separate form configs and edges.

Test plan

• git diff --check
• cd web && npx eslint src/pages/agent/canvas/node/dropdown/accordion-operators.tsx src/pages/agent/constant/pipeline.tsx
• Commit hook ran prettier --write --ignore-unknown and eslint on staged files
• cd web && npm run type-check -- --pretty false currently fails on existing unrelated TypeScript errors outside this change, e.g. src/components/document-preview/doc-preview.tsx, src/components/dynamic-form.tsx, and src/components/file-upload.tsx.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a6af286b-e8ff-4c39-a52b-f5f92863d3dc

📥 Commits

Reviewing files that changed from the base of the PR and between ad4717f and 60afd43.

📒 Files selected for processing (2)

• web/src/pages/agent/canvas/node/dropdown/accordion-operators.tsx
• web/src/pages/agent/constant/pipeline.tsx

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📝 Walkthrough

Walkthrough

This PR modifies operator constraints in the pipeline UI to allow multiple instances of chunker operators. The SingleOperators constant now restricts only tokenizer and parser operators, while chunker operators are handled directly in the accordion component without single-instance filtering.

Changes

Multiple Chunker Operators Support

Layer / File(s)	Summary
Operator singularity constraints web/src/pages/agent/constant/pipeline.tsx	SingleOperators constant is reduced from [Operator.Tokenizer, Operator.TokenChunker, Operator.TitleChunker, Operator.Parser] to [Operator.Tokenizer, Operator.Parser], allowing chunker operators to appear multiple times on the canvas.
Chunker operator handling in accordion web/src/pages/agent/canvas/node/dropdown/accordion-operators.tsx	Comment clarifies that structural pipeline operators must exist at most once, and chunkerOperators is initialized as a fixed [Operator.TokenChunker, Operator.TitleChunker] array without the single-operator restriction filter, enabling multiple instances.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

A rabbit hops through operator trees,
Chunkers now dance in twos and threes—
No longer bound to singular constraint,
Multiple paths the workflow can paint. 🐰✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly and concisely describes the main change: allowing multiple pipeline chunker nodes, which is the primary objective of this changeset.
Description check	✅ Passed	The PR description comprehensively addresses the template sections, explaining the problem solved, changes made, behavioral differences, and test plan.
Linked Issues check	✅ Passed	Code changes directly fulfill issue #14772 by allowing multiple chunker nodes (TokenChunker, TitleChunker) while restricting singleton nodes (Parser, Tokenizer) to single instances, enabling multi-stage classification workflows.
Out of Scope Changes check	✅ Passed	All changes are scoped to the stated objectives: modifying chunker operator filtering logic and updating the SingleOperators constant to reflect the new singleton restrictions.

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