feat(compat): add GCP inventory collection

[nina9753]

Summary

• add GCP Cloud Functions Gen1 identity and inventory metadata collection
• fall back to the GCP metadata server when region or project is absent from the runtime environment
• preserve support for newer Gen1 runtimes that expose K_SERVICE and FUNCTION_TARGET
• detect the platform runtime and version while preserving the explicit compat-runtime handoff

Stack

1. feat(compat): add Azure inventory payload core #175 — Azure identity and core payload
2. GCP inventory collection (this PR)
3. feat(compat): add serverless-compat inventory reporter (SVLS-9604) #161 — reporter, transport, and compat integration

This PR is based on #175. After this slice is approved, #161 will be rebuilt on this branch and remain the top, end-to-end-testable PR so its existing discussion and review history are preserved.

Testing

• cargo test --package datadog-serverless-compat-inventory --locked --offline
• cargo clippy --package datadog-serverless-compat-inventory --all-targets --locked --offline -- -D warnings
• rustfmt --edition 2024 --check on modified Rust sources
• git diff --check

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T14:10:30.446337Z	827586b	PR opened

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[apiarian-datadog]

seems mostly reasonable, tho i'd defer to serverless-compat engineers for a final review.

[Copilot]

Note

Copilot was unable to run its full agentic suite in this review.

Copilot review overview

Review effort: Lite
Findings: 2 · 1 · 1

Open (4)

• platform/gcp.rs calls response.chunk().await, which in reqwest is gated behind the stream… · New
• The new tests use #[tokio::test] (without specifying a flavor), which defaults to the… · New
• Importing QueryEnv from an azure_app_services module in a GCP collector is confusing and… · New
• A new reqwest::Client is built on every metadata lookup. Since the region/project lookups can… · New

What changed in this PR

Adds GCP Cloud Functions platform detection so the serverless compat inventory reporter can emit platform metadata for EnvironmentType::CloudFunction.

Changes:

• Route EnvironmentType::CloudFunction to a new GCP collector.
• Introduce platform/gcp.rs to derive function identity from env vars and (optionally) the GCP metadata server.
• Add new dependencies for HTTP metadata access and async tests.

File	Description
crates/​datadog-serverless-compat-inventory/​src/​platform/​mod.rs	Wires CloudFunction environment type to the new GCP collector.
crates/​datadog-serverless-compat-inventory/​src/​platform/​gcp.rs	Implements GCP Cloud Functions identity + metadata server lookup with unit tests.
crates/​datadog-serverless-compat-inventory/​Cargo.toml	Adds reqwest, tokio, tracing, and httpmock needed by the new collector/tests.

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