docs: add x402 kora demo

[amilz]

Adds a demo for using Kora as a x402 Facilitator:

• includes demo code: client, protected api, facilitator proxy for kora, and kora config
• includes guide

---

Important

Adds a comprehensive demo for integrating x402 with Kora, including code, configuration, and a detailed guide.

• Demo Code:
  • Adds client, protected API, and facilitator proxy code in docs/x402/demo.
  • Facilitator proxy adapts Kora to x402 protocol with /verify, /settle, and /supported endpoints.
  • Protected API uses x402-express middleware to handle payments.
• Configuration:
  • Adds .env.example for environment variables setup.
  • Includes kora.toml and signers.toml for Kora configuration.
• Guide:
  • Provides X402_DEMO_GUIDE.md detailing setup, architecture, and running the demo.
  • Explains x402 protocol, Kora's role, and the payment flow.
• Scripts:
  • Adds scripts in package.json for setup, building, and running the demo components.

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[ellipsis-dev]

Caution

Changes requested ❌

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1. docs/x402/demo/X402_DEMO_GUIDE.md:88

• Draft comment:
  Typo: There is an extra space in the sentence "provides signing and gasless transaction services." Remove the extra space between "and" and "gasless".
• Reason this comment was not posted:
  Decided after close inspection that this draft comment was likely wrong and/or not actionable: usefulness confidence = 10% vs. threshold = 50% While the comment is technically correct about the extra space, this is an extremely minor formatting issue in documentation. The extra space doesn't impact readability or meaning. The rules say not to make comments that are obvious or unimportant. A single extra space in documentation text seems to fall into this category. The extra space could be seen as a small formatting inconsistency that's worth fixing while we're editing the file. Some might argue that maintaining perfect formatting is important for documentation. While clean formatting is good, this level of nitpicking about a single space creates noise in the PR review process and distracts from more substantive issues. The benefit of fixing it is extremely minimal. This comment should be deleted as it points out an extremely minor formatting issue that doesn't meaningfully impact the documentation.

2. docs/x402/demo/X402_DEMO_GUIDE.md:339

• Draft comment:
  Typo: The image path in "" contains a double slash. Please change it to a single slash (e.g. "./assets/x402-protocol-flow.png").
• Reason this comment was not posted:
  Decided after close inspection that this draft comment was likely wrong and/or not actionable: usefulness confidence = 0% vs. threshold = 50% While technically correct that double slashes are unnecessary, they don't actually cause any problems in file paths - both single and double slashes work fine. The image will display correctly either way. This is an extremely minor stylistic issue that doesn't affect functionality. The comment is technically accurate - there is indeed a double slash. And some might argue that clean, consistent file paths are good practice. However, this is an extremely minor stylistic issue that doesn't affect functionality at all. The image will work fine either way. This kind of nitpicky comment creates noise without adding value. This comment should be deleted as it points out an extremely minor stylistic issue that doesn't affect functionality.

3. docs/x402/demo/X402_DEMO_GUIDE.md:409

• Draft comment:
  Typo: The phrase "demonstrates automatic how x402 works" seems off. Consider rephrasing it to something like "demonstrates how x402 works automatically".
• Reason this comment was not posted:
  Decided after close inspection that this draft comment was likely wrong and/or not actionable: usefulness confidence = 10% vs. threshold = 50% While the comment correctly identifies a grammatical error, the PR review rules emphasize focusing on substantive code changes and avoiding purely informative comments. Grammar fixes in documentation, while helpful, are not critical changes that require a comment. The meaning is still clear despite the awkward phrasing. The grammar error does make the documentation slightly less professional. Poor documentation quality could impact user understanding. While documentation quality matters, this is a minor grammatical issue that doesn't significantly impact understanding. The PR review rules specifically discourage non-critical comments. Delete the comment. While the grammar suggestion is valid, it's too minor to warrant a PR comment according to our rules.

4. docs/x402/demo/api/src/api.ts:53

• Draft comment:
  Note: The file does not end with a newline (detected by the \ No newline at end of file marker). Although this might be automatically handled by some formatters, consider adding a trailing newline if your coding standards require it.
• Reason this comment was not posted:
  Comment did not seem useful. Confidence is useful = 0% <= threshold 50% This comment is purely informative and does not provide a specific code suggestion or highlight a potential issue. It simply notes the absence of a newline at the end of the file, which is often automatically handled by formatters. It does not ask for a specific action or confirm an intention, which makes it fall under the category of purely informative comments.

5. docs/x402/demo/client/src/index.ts:18

• Draft comment:
  The error message refers to TEST_SENDER_KEYPAIR, but the code checks for PAYER_PRIVATE_KEY. Please update the environment variable name in the error message for consistency.
• Reason this comment was not posted:
  Marked as duplicate.

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[ellipsis-dev]

Important

Looks good to me! 👍

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1. docs/x402/demo/.env.example:24

• Draft comment:
  Add a newline at the end of the file for POSIX compatibility and best practices.
• Reason this comment was not posted:
  Confidence changes required: 33% <= threshold 50% None

2. docs/x402/demo/X402_DEMO_GUIDE.md:339

• Draft comment:
  Corrected image path by removing an extra slash; ensure the asset exists at './assets/x402-protocol-flow.png'.
• Reason this comment was not posted:
  Confidence changes required: 0% <= threshold 50% None

3. docs/x402/demo/client/src/index.ts:17

• Draft comment:
  Updated error message to refer to PAYER_PRIVATE_KEY, aligning it with the required environment variable.
• Reason this comment was not posted:
  Confidence changes required: 0% <= threshold 50% None

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[dev-jodee]

LFG

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Caution

Changes requested ❌

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1. docs/x402/demo/kora/signers.toml:8

• Draft comment:
  The 'weight = 1' setting has been removed. Verify that this removal is intentional since the documentation sample includes it.
• Reason this comment was not posted:
  Comment was not on a location in the diff, so it can't be submitted as a review comment.

2. docs/x402/demo/package.json:7

• Draft comment:
  The 'install:all' script now chains multiple 'cd' commands with relative paths. This approach can be brittle if the directory structure changes and may benefit from a more robust installation strategy.
• Reason this comment was not posted:
  Decided after close inspection that this draft comment was likely wrong and/or not actionable: usefulness confidence = 20% vs. threshold = 50% While the comment raises a valid concern about maintainability, it's not offering a specific, actionable solution. The pattern of using cd commands is consistent throughout the file and seems to be the established pattern. The comment is more of a general observation than a specific issue requiring immediate action. The comment might be pointing to a real architectural concern that could cause problems during future refactoring. The suggested brittleness could lead to real maintenance issues. While the concern is valid, without proposing a specific, better alternative, this comment doesn't provide actionable value. It's more of a general observation about the codebase's structure. Delete the comment as it doesn't provide specific, actionable feedback and appears to be questioning an established pattern in the codebase rather than addressing a specific issue with the changes.

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