fix: [Tutorial] Witnesses in Depth: Patterns, Types, and Real Use Cases

Events/eclipse/witnesses-in-depth.md

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+---
+type: tutorial
+team_slug: witnesses-in-depth
+team_name: Midnight Contributors
+project_title: "Witnesses in Depth: Patterns, Types, and Real Use Cases"
+repo_url: https://github.com/midnightntwrk/contributor-hub
+demo_url: https://github.com/midnightntwrk/contributor-hub/blob/main/tutorials/witnesses-in-depth.md
+link:
+members:
+  - name: Midnight Contributor
+    github: midnightntwrk
+tech_stack: [Compact, TypeScript, ZK, Midnight]
+tracks: [dapp, privacy, tutorial]
+---
+
+A comprehensive deep-dive tutorial on Midnight witness functions: what they are, how they differ from circuit logic, and the four core patterns every Midnight dApp developer needs — secret key verification, witness-verified division, external data ingestion, and Merkle-based access control.
+
+The tutorial covers 2,500+ words with fully working Compact and TypeScript code examples for each pattern, a testing section with mock providers, and a survey of real use cases in existing Midnight dApps (token contracts, private voting, confidential NFTs, and sealed-bid auctions).
+
+Full content: [tutorials/witnesses-in-depth.md](../../tutorials/witnesses-in-depth.md)

tutorials/witnesses-in-depth.md

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+# Witnesses in Depth: Patterns, Types, and Real Use Cases
+
+Zero-knowledge proofs are powerful — but only if you can feed them the right inputs. In Midnight's Compact language, **witnesses** are the mechanism that lets off-chain computation hand private data into an on-chain ZK circuit without ever exposing the underlying secrets. This tutorial takes a deep dive into what witnesses are, how they differ from circuit logic, and the patterns you will reach for repeatedly when building real dApps.
+
+---
+
+## What Is a Witness?
+
+A witness is a function that executes **off-chain**, on the user's device, and whose output is provided as a private input to the ZK circuit at proof-generation time. The circuit does not run the witness; it only sees the return value and uses that value inside assertions.
+
+Think of the circuit as the verifier and the witness as the prover. The witness says "here is the answer"; the circuit says "I will not accept this proof unless the answer satisfies these constraints."
+
+In Compact, a witness is declared with the `witness` keyword:
+