chore(tracer): add abstract base class for AgentWriterInterface

[brettlangdon]

Preparing the code for a future where we have multiple implementations of the AgentWriter.

I grabbed some minor adjacent type hinting stuff as well.

Split from #13071

We expect no major changes from this change. The only interesting change is the agent_url -> intake_url change which this is an internal/private class.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/_trace/processor/__init__.py                                    @DataDog/apm-sdk-api-python
ddtrace/_trace/tracer.py                                                @DataDog/apm-sdk-api-python
ddtrace/internal/ci_visibility/git_client.py                            @DataDog/ci-app-libraries
ddtrace/internal/ci_visibility/recorder.py                              @DataDog/ci-app-libraries
ddtrace/internal/debug.py                                               @DataDog/apm-core-python
ddtrace/internal/writer/__init__.py                                     @DataDog/apm-core-python
ddtrace/internal/writer/writer.py                                       @DataDog/apm-core-python
ddtrace/opentracer/tracer.py                                            @DataDog/apm-sdk-api-python
tests/appsec/integrations/utils_testagent.py                            @DataDog/asm-python
tests/commands/ddtrace_run_hostname.py                                  @DataDog/apm-core-python
tests/integration/test_debug.py                                         @DataDog/apm-core-python
tests/integration/test_integration.py                                   @DataDog/apm-core-python
tests/integration/test_integration_snapshots.py                         @DataDog/apm-core-python
tests/tracer/test_tracer.py                                             @DataDog/apm-sdk-api-python
tests/tracer/test_writer.py                                             @DataDog/apm-sdk-api-python
tests/utils.py                                                          @DataDog/python-guild

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 284 ± 4 ms.

The average import time from base is: 288 ± 5 ms.

The import time difference between this PR and base is: -3.6 ± 0.2 ms.

Import time breakdown

The following import paths have grown:

ddtrace.auto 0.223 ms (0.08%)

ddtrace.bootstrap.sitecustomize 0.116 ms (0.04%)

ddtrace.bootstrap.preload 0.116 ms (0.04%)

ddtrace.internal.products 0.116 ms (0.04%)

importlib.metadata 0.116 ms (0.04%)

csv 0.116 ms (0.04%)

ddtrace 0.107 ms (0.04%)

ddtrace.trace 0.107 ms (0.04%)

ddtrace._trace.tracer 0.107 ms (0.04%)

ddtrace.internal.processor.endpoint_call_counter 0.107 ms (0.04%)

The following import paths have shrunk:

ddtrace.auto 2.340 ms (0.82%)

ddtrace.bootstrap.sitecustomize 1.537 ms (0.54%)

ddtrace.bootstrap.preload 1.537 ms (0.54%)

ddtrace.internal.remoteconfig.client 0.689 ms (0.24%)

ddtrace.internal.products 0.119 ms (0.04%)

importlib.metadata 0.119 ms (0.04%)

csv 0.119 ms (0.04%)

_csv 0.119 ms (0.04%)

ddtrace 0.803 ms (0.28%)

ddtrace.trace 0.122 ms (0.04%)

ddtrace._trace.tracer 0.122 ms (0.04%)

ddtrace.internal.schema.processor 0.122 ms (0.04%)

ddtrace.internal._unpatched 0.031 ms (0.01%)

json 0.031 ms (0.01%)

json.decoder 0.031 ms (0.01%)

re 0.031 ms (0.01%)

enum 0.031 ms (0.01%)

types 0.031 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-07-10 13:07:26

Comparing candidate commit a328c9b in PR branch LANGPLAT-134/agent-writer-interface with baseline commit b17d958 in branch main.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 547 metrics, 2 unstable metrics.

scenario:iastaspectsospath-ospathjoin_aspect

• 🟥 execution_time [+0.980µs; +1.054µs] or [+15.911%; +17.109%]

[VianneyRuhlmann]

LGTM