feat(BA-2851): Add resource isolation options for multi-agent

[hhoikoo]

resolves #6432 (BA-2851)

This change adds configuration for partitioning resources rather than every agent always seeing the full resource pool. This prevents unintended over-allocation that could crash kernels.

• SHARED: allows all agents to see full resources (useful for stress testing). This is the same behavior as before.
• AUTO_SPLIT: automatically divides resources equally among agents.
• MANUAL: lets users specify exact per-agent allocations for all resources.

Single-agent deployments remain unaffected and retain access to all available hardware resources.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[Copilot]

Pull Request Overview

This PR introduces resource isolation options for multi-agent setups, enabling multiple agents to run on the same physical host with controlled resource allocation. The implementation adds three allocation modes: SHARED (default, backward compatible), AUTO_SPLIT (automatic equal division), and MANUAL (explicit per-agent configuration).

Key changes:

• Introduces ResourcePartitioner class to manage resource allocation across agents
• Adds ResourceAllocationMode enum with SHARED, AUTO_SPLIT, and MANUAL modes
• Implements validation logic to ensure consistent manual allocations across agents
• Updates agent initialization to use resource partitioning

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 23 comments.

Show a summary per file

File	Description
src/ai/backend/agent/resources.py	Adds ResourcePartitioner class and changes abstract methods to raise NotImplementedError
src/ai/backend/agent/config/unified.py	Defines allocation modes, new config fields (allocated_cpu/mem/disk/devices), and validation logic
src/ai/backend/agent/agent.py	Integrates ResourcePartitioner into agent initialization and updates slot calculations
src/ai/backend/agent/server.py	Creates ResourcePartitioner instances per agent and adds resource reconciliation
src/ai/backend/agent/docker/agent.py	Adds resource_partitioner parameter to constructor
src/ai/backend/agent/kubernetes/agent.py	Adds resource_partitioner parameter to constructor
tests/agent/test_resource_allocation.py	Comprehensive unit tests for all three allocation modes
tests/agent/test_config_validation.py	Tests for config validation of allocation modes and device consistency
tests/agent/docker/test_agent.py	Updates test to pass ResourcePartitioner to agent
changes/6498.feature.md	Changelog entry

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