fix(session-manager): eliminate session manager double-folder bug

[galuszkm]

Description

Problem
The session manager was being resolved twice at boot time, creating orphan
folders:

1. Once in resolve_infra() (before session_id is known) → random UUID folder
2. Again in load_session() (with real session_id) → correct folder
   Result: one empty orphan folder per process startup.

Solution
Move session manager resolution from infra/load_session to the leaves (per-agent and per-orchestration builders). A single effective_session_id is computed once in load_session() and threaded down, ensuring all agents in one session share the same session_id and storage backend.

Related Issues

N/A

Type of Change

• Bug fix
• Breaking change

YAML / API Impact

Essential Changes

• Removed ResolvedInfra.session_manager field (pure infra, no I/O)
• resolve_infra() validates global SM config only (rejects agentcore globally)
• load_session() computes effective_session_id and threads it down
• All leaf builders now accept global_session_manager_def + session_id params
• New helper resolve_leaf_session_manager() implements uniform 4-step chain:
  1. Agent/orch-level def (if set)
  2. Explicit opt-out (if field is explicitly None)
  3. Global def (fallback)
  4. None (no session persistence)
• build_delegate merges orch session_manager into forked entry_def
• build_swarm / build_graph resolve leaf SM inline before building

Breaking Changes

• ResolvedInfra.session_manager removed entirely
• Function signatures changed: resolve_agents(), build_agent_from_def(), OrchestrationBuilder.__init__(), build_delegate(), build_swarm(), build_graph(), and resolve_orchestrations() no longer accept session_manager= parameter; use keyword-only global_session_manager_def + session_id instead
• session_manager_override parameter removed from build_agent_from_def()
• Each agent/orchestration now resolves its own SM instance (not shared across agents); functionally identical for file/S3/AgentCore providers which have no shared in-memory state

Testing

How have you tested the change?

• I ran uv run just check (lint + type check)
• I ran uv run just test for overall testing
• I added or updated tests that prove my fix is effective or my feature works
• I verified existing examples in examples/ still work

Checklist

• I have read the CONTRIBUTING document
• I have updated the documentation accordingly
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[Copilot]

Pull request overview

This PR fixes a boot-time session manager double-resolution that created an orphan session folder by deferring session manager instantiation to per-agent / per-orchestration “leaf” builders and threading a single effective_session_id through load_session().

Changes:

• Removed ResolvedInfra.session_manager and changed resolve_infra() to validate (but not construct) global session manager configuration.
• Added effective_session_id computation in load_session() and passed global_session_manager_def + session_id down into agent/orchestration builders.
• Introduced a shared resolve_leaf_session_manager() helper to enforce consistent precedence (leaf override → explicit opt-out → global fallback → none), and updated tests/docs accordingly.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
uv.lock	Bumps local package version to 0.3.0 in the lockfile.
tests/unit/test_exception_usage.py	Removes unnecessary ty: ignore on topological_sort calls.
tests/unit/config/resolvers/test_config.py	Updates infra tests for “no session manager construction in resolve_infra” and adds global agentcore rejection test.
tests/unit/config/resolvers/test_agents.py	Updates agent resolver tests for new global_session_manager_def + session_id plumbing and leaf resolution behavior.
tests/unit/config/resolvers/orchestrations/test_planner.py	Removes unnecessary ty: ignore on topological_sort calls.
tests/unit/config/resolvers/orchestrations/test_builders.py	Updates orchestration builder tests for new SM def/session_id wiring; adds additional session-id forwarding assertions.
tests/unit/config/loaders/test_load_session.py	Updates load_session() tests to validate effective_session_id derivation and def/session_id threading.
src/strands_compose/config/resolvers/session_manager.py	Adds resolve_leaf_session_manager() helper implementing the uniform leaf precedence chain.
src/strands_compose/config/resolvers/orchestrations/planner.py	Broadens topological_sort input type to Mapping for better flexibility.
src/strands_compose/config/resolvers/orchestrations/builders.py	Moves session manager resolution into leaf builders; threads global_session_manager_def + session_id.
src/strands_compose/config/resolvers/orchestrations/init.py	Updates orchestration resolver signature to accept global_session_manager_def + session_id.
src/strands_compose/config/resolvers/config.py	Removes ResolvedInfra.session_manager and changes resolve_infra() to SM validation-only.
src/strands_compose/config/resolvers/agents.py	Resolves session managers via resolve_leaf_session_manager() and updates resolver signatures.
src/strands_compose/config/loaders/loaders.py	Computes effective_session_id and threads it + global SM def into leaf resolvers.
docs/configuration/Chapter_17.md	Documents new infra/session behavior and effective_session_id semantics.
docs/configuration/Chapter_07.md	Updates guidance to reflect single effective session id per load_session() call.