fix: pin a2a-sdk below 1.0 to prevent breaking changes

[aidandaly24]

Description

The a2a-python SDK recently released v1.0.0 which upgrades from the 0.3 protocol spec to the 1.0 protocol spec. This introduces breaking changes to module paths and APIs that our A2A templates depend on (e.g., a2a.server.agent_execution, a2a.types, a2a.utils).

Since our templates specify a2a-sdk >= 0.2.0 with no upper bound, pip install now resolves to 1.0.x, breaking all agentcore create --protocol A2A projects.

This PR adds < 1.0.0 upper bound to all three A2A template pyproject.toml files so pip resolves to 0.3.26 (latest compatible version).

Files changed:

• src/assets/python/a2a/googleadk/base/pyproject.toml
• src/assets/python/a2a/strands/base/pyproject.toml
• src/assets/python/a2a/langchain_langgraph/base/pyproject.toml
• Snapshot updated accordingly

Related Issue

Closes #1147

Documentation PR

N/A — no documentation changes needed.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the
terms of your choice.

[agentcore-cli-automation]

Reviewed the diff — this looks good to merge.

Verified:

• Templates import from a2a.server.agent_execution, a2a.server.events, a2a.server.tasks, a2a.types, and a2a.utils, which are the 0.3-era paths that the PR description says broke in 1.0, so the upper bound is warranted.
• The < 1.0.0 constraint is applied to all three A2A templates (googleadk, langchain_langgraph, strands), the [all] extra on strands is preserved, and the snapshot is updated consistently.
• Confirmed against PyPI that the highest stable release under 1.0 is 0.3.26, so pip will resolve to a working version.
• No other references to a2a-sdk elsewhere in src/ that would need a matching pin.

No blocking issues.

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	43.1%	9015 / 20912
🔵	Statements	42.39%	9573 / 22582
🔵	Functions	39.91%	1553 / 3891
🔵	Branches	39.98%	5808 / 14527

Generated in workflow #2562 for commit 42487c0 by the Vitest Coverage Report Action