chore(main): release 2.26.0 - #3002

🤖 I have created a release beep boop

2.26.0 (2026-09-30)

Features

• Add gcs_metrics_uri for exporting tuning job metrics. (b6535e8)
• Add Gemini 3.8 Flash TTS and Gemini 3.8 Flash Lite TTS models to SDKs (0cad6ca)
• genai-sdk: Add environments dedicated module and from_environment support (7672ff6)
• Include labels for LiveClientSetup (4742c9a)
• Support labels for Gemini API GenerateContent (81ffa26)

Bug Fixes

• Build a model before reading its field annotations when pruning extra fields (7845acd)
• cli: Include auto-assigned flag shorthands in --usage schema (2579b94)
• Ensure Vertex AI interactions client uses default timeout=None instead of 5s. (feef230)
• Reap aiohttp sessions and auth locks belonging to closed event loops (6d01288)
• Use CreateAgentInteraction for Trigger.interaction and TriggerCreateParams.interaction (046ccfb)

Documentation

• Clarify Voice expire_time and store TTL behavior in GAOS SDK (94b371d)
• overlays: Describe environment and path on GetEnvironmentFiles and pin environment ID in environments get/delete examples (f15d148)
• Regenerate docs for 1.2.0 (938dd73)

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