Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

# Description

This PR introduces a new feature allowing server maintainers to provide
custom ID generators for system-created objects.

I identified 2 key areas requiring ID generation:
-
[`ResourceContext`](https://github.com/a2aproject/a2a-python/blob/19091262d07b5226becdb177ed4d780b4befb5f4/src/a2a/server/agent_execution/context.py):
Manages the creation of new task and context IDs when not supplied by
the client.
-
[`TaskUpdater`](https://github.com/a2aproject/a2a-python/blob/19091262d07b5226becdb177ed4d780b4befb5f4/src/a2a/server/tasks/task_updater.py):
Helper responsible for generating IDs for new artifacts and messages
during task updates.

To address this, a new abstract class, `IDGenerator`, has been
introduced. This class enables the creation of specific ID generators
for different resource types, which can then be integrated into the
relevant SDK components.

Alternative approaches were considered:
1. Using a single `IDGenerator` instance for all resource types, with
resource type information passed to the generate method. This option was
discarded due to potential coupling issues and increased maintenance
complexity.
1. Implementing an additional `IDGeneratorRegistry` to manage
per-resource-type generators via a `get_id_generator(resource_type)`
method. While this would simplify object passing, it introduces
additional indirection and overall system complexity.

# Prerequisites
- [x] Follow the [`CONTRIBUTING`
Guide](https://github.com/a2aproject/a2a-python/blob/main/CONTRIBUTING.md).
- [x] Make your Pull Request title in the
<https://www.conventionalcommits.org/> specification.
- Important Prefixes for
[release-please](https://github.com/googleapis/release-please):
- `fix:` which represents bug fixes, and correlates to a
[SemVer](https://semver.org/) patch.
- `feat:` represents a new feature, and correlates to a SemVer minor.
- `feat!:`, or `fix!:`, `refactor!:`, etc., which represent a breaking
change (indicated by the `!`) and will result in a SemVer major.
- [x] Ensure the tests and linter pass (Run `bash scripts/format.sh`
from the repository root to format)
- [x] Appropriate docs were updated (if necessary)

Fixes #378 🦕

---------

Co-authored-by: lkawka <lkawka@google.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Holt Skinner <13262395+holtskinner@users.noreply.github.com>

… `agent_card_path` when `relative_card_path` is empty (#508)

- Previously, it would only override with the default path when
`relative_card_path` is `None`
- Developer Experience Improvement when `urlparse` or similar libraries
are used.

# Description

changes to honor `historyLength` param passed for `message/send`
requests

Fixes #497  🦕

Release-As: 0.3.9

🤖 I have created a release *beep* *boop*
---


##
[0.3.9](v0.3.8...v0.3.9)
(2025-10-15)


### Features

* custom ID generators
([051ab20](051ab20))


### Bug Fixes

* apply `history_length` for `message/send` requests
([#498](#498))
([a49f94e](a49f94e))
* **client:** `A2ACardResolver.get_agent_card` will auto-populate with
`agent_card_path` when `relative_card_path` is empty
([#508](#508))
([ba24ead](ba24ead))


### Documentation

* Fix Docstring formatting for code samples
([#492](#492))
([dca66c3](dca66c3))

---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).