Fixing URL Synthesis: A Developer's Guide To Deterministic Output

Aug 12, 2025 by Luna Greco 66 views

Fix URL Source in Synthesized Output: A Comprehensive Guide

2. Fixing the Hacker News URL in Synthesis

Options Analysis

Option A: Pass URL to AI in the prompt

Pros: Most accurate, AI can reference it naturally
Cons: Uses more tokens, might still get ignored

Option B: Append URL after AI generation

Pros: 100% reliable, simple to implement
Cons: Might feel less integrated

Option C: Post-process AI output to inject URL

Pros: Seamless integration if AI mentions "PROVENANCE"
Cons: More complex pattern matching

Exact Code Changes

File: `src/services/geminiService.ts`

Step 1: Add a helper function after the streamSynthesis function (around line 110):

// Helper to ensure HN URL is in provenance
function ensureHnUrlInContent(content: string, hnUrl?: string): string {
 if (!hnUrl) return content;
 
 // Check if there's already a PROVENANCE section
 const provenanceMatch = content.match(/##\s*PROVENANCE/i);
 
 if (provenanceMatch) {
 // Check if HN URL is already there
 if (content.includes(hnUrl)) return content;
 
 // Add HN URL to existing PROVENANCE section
 const provenanceIndex = content.indexOf(provenanceMatch[0]);
 const afterProvenance = content.substring(provenanceIndex + provenanceMatch[0].length);
 const nextHeaderIndex = afterProvenance.search(/\n##\s/);
 
 if (nextHeaderIndex === -1) {
 // PROVENANCE is the last section
 return content + `\n- Hacker News Discussion: ${hnUrl}`;
 } else {
 // Insert before next section
 const insertPoint = provenanceIndex + provenanceMatch[0].length + nextHeaderIndex;
 return content.slice(0, insertPoint) + `\n- Hacker News Discussion: ${hnUrl}` + content.slice(insertPoint);
 }
 } else {
 // No PROVENANCE section, add one
 return content + `\n\n## PROVENANCE\n- Hacker News Discussion: ${hnUrl}`;
 }
}

Step 2: Modify the streamSynthesis function to accept optional HN URL:

Find this function signature (around line 95):

export async function streamSynthesis(
 content1: string,
 content2: string,
 model: ModelId,
 onUpdate: (partial: string) => void
): Promise<string> {

Replace with:

export async function streamSynthesis(
 content1: string,
 content2: string,
 model: ModelId,
 onUpdate: (partial: string) => void,
 hnUrl?: string
): Promise<string> {

Then at the end of the same function, find:

 return full;
}

Replace with:

 return ensureHnUrlInContent(full, hnUrl);
}

File: `src/App.tsx`

Find the runFull function (around line 200), locate this line:

const fullSyn = await streamSynthesis(c1, c2, model, setSynthesisBuf);

Replace with:

const fullSyn = await streamSynthesis(c1, c2, model, setSynthesisBuf, hnUrl || undefined);

Commands to Test and Deploy

# 1. Build the updated site
npm run build

# 2. Test locally
npm run preview
# Open http://localhost:4173/ and test with a Hacker News URL

# 3. If working correctly, deploy
npm run deploy

Testing Instructions

To verify the HN URL fix:

Go to your local preview
Paste a Hacker News URL like https://news.ycombinator.com/item?id=12345
Choose "Full Analysis"
Check that the synthesis includes the HN URL in the PROVENANCE section at the bottom

The changes are minimal and safe - they only add information without breaking existing functionality. The helper function gracefully handles all cases: when there's already a PROVENANCE section, when there isn't one, and when there's no HN URL at all.

Of course! I'd be happy to help you with your project, Synthi. It looks like a fantastic tool. Here are the detailed instructions to make the changes you've requested.

Part 1: Changing the Website URL to `synthi.civics.com`

To change the live URL of your application, you'll need to update configuration files that tell your build tools and the browser where the site lives. Here are all the locations in the code you'll need to modify.

File 1: `package.json`

File Location: prototypejam-synthesize/package.json
Reason for Change: The homepage field is used by the gh-pages deployment tool to determine the final URL. It also helps build tools set the correct public path for your assets.
Instructions: Replace the "homepage" line with the new URL.

Replace this block:

 "homepage": "https://prototypejam.github.io/synthesize/",

With this new block:

 "homepage": "https://synthi.civics.com",

File 2: `vite.config.ts`

File Location: prototypejam-synthesize/vite.config.ts
Reason for Change: The base property in your Vite configuration tells the build process what the root path of the application is. Since you are moving from a sub-directory (/synthesize/) to the root of a domain (/), this must be updated to '/'. This ensures that links to your JavaScript and CSS files work correctly.
Instructions: Change the base property from '/synthesize/' to '/'.

Replace this block:

// https://vitejs.dev/config/
export default defineConfig({
 base: '/synthesize/',
 plugins: [react()],
})

With this new block:

// https://vitejs.dev/config/
export default defineConfig({
 base: '/',
 plugins: [react()],
})

File 3: `public/manifest.json`

File Location: prototypejam-synthesize/public/manifest.json
Reason for Change: The scope property in the Web App Manifest defines the navigation scope of the PWA. By changing it from "/synthesize/" to "/", you are allowing your PWA to apply to the entire domain, which is correct for the new URL.
Instructions: Update the scope value.

Replace this block:

{
 "short_name": "Synthi",
 "name": "Synthi — URL Content Synthesizer",
 "icons": [
 { "src": "icon-192.png", "type": "image/png", "sizes": "192x192" },
 { "src": "icon-512.png", "type": "image/png", "sizes": "512x512" }
 ],
 "start_url": ".",
 "scope": "/synthesize/",
 "display": "standalone",
 "theme_color": "#111827",
 "background_color": "#111827"
}

With this new block:

{
 "short_name": "Synthi",
 "name": "Synthi — URL Content Synthesizer",
 "icons": [
 { "src": "icon-192.png", "type": "image/png", "sizes": "192x192" },
 { "src": "icon-512.png", "type": "image/png", "sizes": "512x512" }
 ],
 "start_url": ".",
 "scope": "/",
 "display": "standalone",
 "theme_color": "#111827",
 "background_color": "#111827"
}

File 4: `README.md`

File Location: prototypejam-synthesize/README.md
Reason for Change: The README.md file contains a prominent link to the live version of your application. You should update this to point to the new domain so users can find your project.
Instructions: Find the line with the "Try Synthi Live!" link and replace the URL.

Replace this line:

**[➡️ Try Synthi Live!](https://prototypejam.github.io/synthesize/)**

With this new line:

**[➡️ Try Synthi Live!](https://synthi.civics.com)**

Commands to Rebuild, Test, and Deploy

After making the code changes above, open your terminal in VS Code on your Mac and follow these steps.

Install Dependencies: If you haven't already, make sure all project dependencies are installed.

npm install

Build the Static Site: This command runs Vite to compile your React and TypeScript code into a static dist folder.

npm run build

Test the Build Locally: Before deploying, you can preview the production version of your site to make sure everything works correctly with the new URL configuration.

npm run preview

Your terminal will provide a local URL (e.g., http://localhost:4173). Open this in your browser to test the site.

Deploy to GitHub Pages: Once you've confirmed the local preview works, run this command to push the contents of your dist folder to the gh-pages branch of your repository.

npm run deploy

Final Step (Outside of Code): For synthi.civics.com to work, you must configure it as a custom domain in your GitHub repository's settings under "Pages". This involves adding the domain there and setting up the necessary DNS records (e.g., CNAME or A records) with your domain registrar.

Stop the HN URL from being hallucinated; always append the real link

You already capture the real Hacker News thread URL in state (hnUrl) and even persist it in history and front‑matter on export; the missing piece is deterministically adding a footer to the synthesized text itself so it shows up in the UI and in exported Markdown even if the model omits or misstates it.

Options

UI‑level post‑processing (append a provenance footer in App.tsx after synthesis) — recommended

Mechanism: After streamSynthesis finishes, append a ## PROVENANCE (or ## VERIFIED LINKS if the model already added one) with real URLs: Source 1, Source 2, and Hacker News.
Pros: One small change; works for on‑screen view and downloads; zero prompt dependency; no API churn.
Cons: The extra footer appears only after streaming completes (not during the stream).

Pass canonical URLs into the prompt (SYNTHESIS_PROMPT) so the model quotes them

Pros: Keeps content “pure” from the model.
Cons: Still model‑dependent; requires changing streamSynthesis signature to pass URLs through and touching multiple files.

Render‑only footer in the UI (e.g., add a “Provenance” block below the synthesis card without changing the text)

Pros: Zero interaction with the model/results.
Cons: Footer disappears from downloaded Markdown, which you likely don’t want.

Recommendation

Go with Option 1: append a deterministic footer in App.tsx after synthesis completes. Low risk, simple, and it guarantees the on‑screen and exported text always contains the true HN URL (and both source URLs).

Exact code changes (copy/paste)

All edits are in src/App.tsx.

Add a helper inside the App component to append the footer. Insert this right after your existing useState hooks for URLs/HN (for a precise spot, put it immediately after const [hnUrl, setHnUrl] = useState<string | null>(null);):

 // Append a deterministic provenance footer to synthesis content
 const appendProvenance = useCallback((content: string) => {
 const links: string[] = [];
 if (inputType1 === 'url' && url1) links.push(`- Source 1: ${url1}`);
 if (mode === 'dual' && inputType2 === 'url' && url2) links.push(`- Source 2: ${url2}`);
 if (hnUrl) links.push(`- Hacker News: ${hnUrl}`);
 if (links.length === 0) return content;

 const hasProv = /(^|\n)##\s*PROVENANCE\b/i.test(content);
 const header = hasProv ? '## VERIFIED LINKS' : '## PROVENANCE';
 return `${content.trim()}\n\n${header}\n${links.join('\n')}\n`;
 }, [inputType1, inputType2, url1, url2, hnUrl, mode]);

Reason: Builds a footer from the actual URLs in state, avoiding any model guesswork.

Use the helper in the “full” flow. In runFull, replace the two lines that set synthesis with this block:

Find this in runFull:

 const fullSyn = await streamSynthesis(c1, c2, model, setSynthesisBuf);
 setResults({ summary1: full1, summary2: full2, synthesis: fullSyn });

Replace with:

 const fullSyn = await streamSynthesis(c1, c2, model, setSynthesisBuf);
 const fullSynWithProv = appendProvenance(fullSyn);
 setResults({ summary1: full1, summary2: full2, synthesis: fullSynWithProv });

And update the history.add call a few lines below so it stores the footer‑augmented synthesis:

Find:

 results: { summary1: full1, summary2: full2, synthesis: fullSyn },

Replace with:

 results: { summary1: full1, summary2: full2, synthesis: fullSynWithProv },

Reason: Ensures both the on‑screen synthesis and the saved history contain the verified URLs.

Use the helper in the mixed‑mode branch (the handleRun else‑path where one or both sources are pasted). Replace the two lines that set synthesis with:

Find in the mixed‑mode try block:

 const syn = await streamSynthesis(c1, c2, model, setSynthesisBuf);
 setResults({ summary1: full1, summary2: full2, synthesis: syn });

Replace with:

 const syn = await streamSynthesis(c1, c2, model, setSynthesisBuf);
 const synWithProv = appendProvenance(syn);
 setResults({ summary1: full1, summary2: full2, synthesis: synWithProv });

Reason: Same guarantee for synthesis when sources include pasted text.

That’s the only code you need to touch to stop the HN URL from being hallucinated. You do not need to change the prompts or geminiService.ts for this fix (though passing URLs into the prompt would be a valid alternative if you want the model to speak them earlier).

Rebuild, test, deploy (commands)

From the repo root in VS Code’s terminal:

# Build & preview the updated app locally
npm install
npm run build
npm run preview
# Open http://localhost:4173/ and run a synthesis on any HN thread.
# Scroll to the bottom of the Synthesis card and you should see:
# ## PROVENANCE
# - Source 1: ...
# - Source 2: ...
# - Hacker News: https://news.ycombinator.com/item?id=...

# Commit and deploy
git add -A
git commit -m "Append deterministic provenance with canonical HN URL"
npm run deploy

# Verify live
open https://synthi.civics.com

(Optional) If you also want the model to say the exact HN URL

If you later want the LLM itself to include the true URL in its prose, change the streamSynthesis signature to accept hnThreadUrl and prepend it into the contents you send (and pass hnUrl from App.tsx). This touches a few places (geminiService.ts, App.tsx call sites) and is more invasive, which is why I recommend the simple footer approach above first.

If you want me to give you a “support both” setup (one build for prototypejam.github.io/synthesize/ and another for synthi.civics.com using an env variable to flip Vite’s base), say the word and I’ll lay out the exact diffs and build commands.

2. Fixing the Hacker News URL in Synthesis

Options Analysis

Option A: Pass URL to AI in the prompt

Option B: Append URL after AI generation

Option C: Post-process AI output to inject URL

Recommended Solution: Option B + Smart Integration

Exact Code Changes

File: src/services/geminiService.ts

File: src/App.tsx

Commands to Test and Deploy

Testing Instructions

Part 1: Changing the Website URL to synthi.civics.com

File 1: package.json

File 2: vite.config.ts

File 3: public/manifest.json

File 4: README.md

Commands to Rebuild, Test, and Deploy

Stop the HN URL from being hallucinated; always append the real link

Options

Recommendation

Exact code changes (copy/paste)

Rebuild, test, deploy (commands)

(Optional) If you also want the model to say the exact HN URL

File: `src/services/geminiService.ts`

File: `src/App.tsx`

Part 1: Changing the Website URL to `synthi.civics.com`

File 1: `package.json`

File 2: `vite.config.ts`

File 3: `public/manifest.json`

File 4: `README.md`