feat(binding): add per-request strict JSON binding (JSONStrict)

[walle250ai]

Summary

The existing global flag is not safe for concurrent use: toggling it affects all in-flight requests, making per-endpoint strict validation impossible without race conditions.

This PR adds a request-scoped strict JSON binding path:

• — new that always enables , independent of the global flag
• — returns error on unknown fields, does not abort
• — aborts with HTTP 400 on any binding error including unknown fields

The existing behavior and are untouched.

Test plan

• : valid payload, unknown fields (must error), empty body, invalid JSON, independence from global flag
• : HTTP-layer behavior of (400 on unknown fields/invalid JSON/empty body) and (error returned, no abort)
• All 13 new tests pass:

🤖 Generated with Claude Code

[Qodo-Free-For-OSS]

Hi, Context.BindJSONStrict/ShouldBindJSONStrict reference binding.JSONStrict, but the nomsgpack build variant does not define that symbol, so builds with -tags nomsgpack will not compile.

Severity: action required | Category: correctness

How to fix: Define JSONStrict for nomsgpack

Agent prompt to fix - you can give this to your LLM of choice:

Issue description

Building with -tags nomsgpack fails because context.go references binding.JSONStrict but the nomsgpack binding variant doesn’t define it.

Issue Context

• binding/binding.go is guarded by //go:build !nomsgpack.
• In nomsgpack builds, binding/binding_nomsgpack.go is used instead and currently lacks a JSONStrict variable.

Fix Focus Areas

• binding/binding_nomsgpack.go[71-88]
• context.go[767-884]

What to change

• Add JSONStrict = jsonStrictBinding{} (typed consistently with the other vars in this file) into the var (...) block in binding/binding_nomsgpack.go.
• Ensure it implements the same interfaces as JSON in nomsgpack builds (it should, since jsonStrictBinding has Bind and BindBody).

We noticed a couple of other issues in this PR as well - happy to share if helpful.

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