chore: import upstream snapshot with attribution

docs/articles/c-interop.md

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+## The C Boundary
+
+Zerolang supports a small explicit C ABI surface from graph inputs. C-facing code
+should stay narrow, inspectable, and target-aware.
+
+```json-render
+{
+  "messages": [
+    {
+      "role": "user",
+      "text": "can this call my tiny c helper on linux musl?"
+    },
+    {
+      "role": "assistant",
+      "text": "I’ll check the target link plan and tell you what blocks the call."
+    },
+    {
+      "role": "tools",
+      "calls": [
+        {
+          "command": "zero inspect --json --target linux-musl-x64",
+          "output": "{\"cLibraries\":[{\"linkPlan\":{\"sysrootStatus\":\"configured\"}}]}"
+        }
+      ]
+    }
+  ]
+}
+```
+
+## What This Means
+
+Projection example:
+
+```zero
+export c fn add(a: i32, b: i32) -> i32 {
+    return a + b
+}
+```
+
+Graph checks:
+
+```sh
+zero check conformance/native/pass/c-abi-export.graph
+zero abi dump --json conformance/native/pass/c-abi-export.graph
+```
+
+`zero abi dump --json` reports exported symbols and generated header facts such
+as `generatedHeader.available`.
+
+## Import Metadata
+
+Header imports expose typed metadata:
+
+```sh
+zero inspect --json --target linux-musl-x64 conformance/check/pass/c-header-import.graph
+```
+
+The JSON includes `cImports[].typedModel` with imported functions, constants,
+structs, enums, and typedefs.
+
+Callable imports are limited to direct scalar ABI types today: `Void`, `Bool`,
+`u8`, `u16`, `usize`, `i32`, `u32`, `i64`, and `u64`. Pointer, array, struct,
+and unsupported-width parameters should be wrapped by a small C shim.
+
+## Link Plans
+
+Executable builds with direct extern C calls require package link metadata in
+`zero.toml`. Imported headers must appear in `c.libs.*.headers`, and the
+library must provide `lib` or `link` inputs.
+
+`zero inspect --json` reports each `cLibraries[].linkPlan` with include paths,
+library paths, sysroot status, target ABI, host discovery status, and header
+hash data.
+
+Unsafe foreign-target discovery fails with `CIMP003`. Missing or unsafe link
+inputs fail with `CIMP005`.