Исправить project_id Gemini из ADC

[konard]

Fixes #2499

Problem

Gemini is the default AI provider and uses the Vertex AI OpenAI-compatible endpoint with {project_id}. The server only looked for that project id in explicit provider settings or env variables, so a valid ADC setup with project_id in GOOGLE_APPLICATION_CREDENTIALS_JSON or the credentials file still failed with {"error":"Не указан Google Cloud project_id для Gemini"}.

Solution

• Read projectId, project_id, or googleProjectId from the merged provider config before falling back to saved profile settings.
• Keep existing env support and add CLOUDSDK_CORE_PROJECT.
• Discover the project id from ADC JSON, ADC credentials files, and GCE metadata (project/project-id).
• Add a regression experiment covering direct provider config, ADC JSON, and ADC credentials file cases.
• Remove the generated .gitkeep placeholder from the PR diff.
• Merge the latest origin/main into this branch after PR Добавить подсказку к полю проверки уникальности #2498 landed.

Reproduce

Before this change, php experiments/test-issue-2499-gemini-project-id.php fails with the reported Gemini project_id error even when ADC JSON contains project_id.

After this change, the Gemini endpoint is prepared with /projects/<id>/... and no {project_id} placeholder remains.

Tests

• php experiments/test-issue-2499-gemini-project-id.php
• node experiments/test-issue-2483-ai-chat-server.js
• node experiments/test-issue-2481-ai-providers.js
• node experiments/test-issue-2491-ai-chat-current-db.js
• node experiments/test-issue-2495-unique-key-ui.js
• node experiments/test-issue-2486-ai-chat-local-storage.js
• node experiments/test-issue-2471-ai-chat.js
• node experiments/test-issue-2474-ai-chat-global.js
• node experiments/test-issue-2488-ai-chat-button-border.js
• node --check js/ai-chat.js
• php -l index.php
• php -l experiments/test-issue-2499-gemini-project-id.php
• git diff --check origin/main...HEAD

[konard]

Working session summary

Implemented and pushed the fix to PR 2500: #2500

Changed index.php so Gemini can resolve project_id from merged provider config, env, ADC JSON, ADC credentials files, or GCE metadata. Added regression coverage in experiments/test-issue-2499-gemini-project-id.php.

Verified with the AI chat/provider tests, PHP syntax checks, the new regression test, and git diff --check origin/main...HEAD. The branch is clean, includes latest origin/main, PR is ready for review, and GitHub reports no configured status checks/runs for this branch.

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[konard]

🤖 Solution Draft Log

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💰 Cost estimation:

• Model: GPT-5.5
• Provider: OpenAI
• Public pricing estimate: $5.607788

📊 Context and tokens usage:

• 142.1K / 1.1M (14%) input tokens, 20.6K / 128K (16%) output tokens

Total: (142.1K + 3.3M cached) input tokens, 20.6K output tokens, $5.607788 cost

🤖 Models used:

• Tool: OpenAI Codex
• Requested: gpt-5.5
• Model: GPT-5.5 (gpt-5.5)

📎 Log file uploaded as Gist (24166KB)

• View complete solution draft log

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[konard]

✅ Ready to merge

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