[Based on #108] debug: add typed artifact modes and Wasm sidecars

[cpunion]

Implements the typed debug-artifact part of xgo-dev#2164 on top of #108.

Problem

After a target can retain DWARF, the build still cannot distinguish embedded, host-owned, external, and omitted debug artifacts. Wasm also has no standards-based way to publish a deployable module with debugger metadata in a sidecar.

Changes

• add -debug-artifact=embedded|external|host|none and resolve it into typed -w intent without changing the current safe default;
• keep debug-artifact selection independent of pclntab selection;
• implement the WebAssembly external_debug_info convention with an adjacent URL-escaped .debug.wasm sidecar;
• preserve every standard Wasm section byte-for-byte in the deployable module while removing embedded DWARF/relocation sections;
• atomically publish sidecar and main artifacts, and remove stale sidecars on non-external rebuilds and llgo clean;
• add an Ubuntu/Go 1.26 CI check that builds real LLGo embedded and external Wasm artifacts and inspects their final sections.

The external sidecar is the complete linked debug module, which the WebAssembly convention permits and which preserves the exact code/data layout used by DWARF. Runtime pclntab packaging is unchanged.

Verification

• macOS full related-package suite (excluding the pre-existing hanging stdio test): 76.0% statement coverage;
• macOS and Linux/amd64 focused tests: internal/wasmdebug 94.3%, all new flag/policy/finalization tests pass;
• real LLGo WASI builds on macOS and Linux/amd64 verify:
  • embedded module contains .debug_info;
  • external main contains external_debug_info and no .debug_info;
  • sidecar contains .debug_info;
  • rebuilding the same output with none removes the stale sidecar.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[github-actions]

LLGo baseline benchmarks

0f6a37f15b28 | workflow run | long-term charts

Program measurements

Platform	Workload	File size	vs main	Build	vs main	Run	vs main
Linux	cprintf	18544 B	+0.0%	327.002 ms	-20.7% (better)	1.226 ms	-21.0% (better)
Linux	fmtprintf	2217600 B	+0.2% (worse)	3.223 s	-16.4% (better)	2.414 ms	-26.6% (better)
Linux	println	71504 B	-1.6% (better)	332.235 ms	-17.0% (better)	1.561 ms	-6.7% (better)
macOS	cprintf	84672 B	+0.0%	332.763 ms	-19.7% (better)	2.376 ms	-33.8% (better)
macOS	fmtprintf	2361520 B	+0.7% (worse)	2.568 s	-34.8% (better)	16.349 ms	-30.1% (better)
macOS	println	125712 B	-1.0% (better)	321.135 ms	-22.5% (better)	3.664 ms	-49.5% (better)

Core language and compiler benchmarks

Platform	Benchmark	ns/op	vs main
Linux	BenchmarkLookupPCRandom	13.410 ns/op	-0.5% (better)
Linux	BenchmarkMergeCompilerFlags	153.600 ns/op	-0.6% (better)
Linux	BenchmarkMergeLinkerFlags	98.700 ns/op	-2.6% (better)
Linux	BenchmarkChannelBuffered	33.980 ns/op	-2.2% (better)
Linux	BenchmarkChannelHandoff	25617 ns/op	-20.0% (better)
Linux	BenchmarkDefer	42.230 ns/op	-25.0% (better)
Linux	BenchmarkDirectCall	1.555 ns/op	-0.5% (better)
Linux	BenchmarkGlobalRead	1.869 ns/op	+19.8% (worse)
Linux	BenchmarkGlobalWrite	2.485 ns/op	-0.4% (better)
Linux	BenchmarkGoroutine	30767 ns/op	-59.3% (better)
Linux	BenchmarkInterfaceCall	8.091 ns/op	+3.8% (worse)
Linux	BenchmarkRuntimeGetG	1.870 ns/op	-64.8% (better)
macOS	BenchmarkLookupPCRandom	11.430 ns/op	-8.1% (better)
macOS	BenchmarkMergeCompilerFlags	92.380 ns/op	-25.8% (better)
macOS	BenchmarkMergeLinkerFlags	61.630 ns/op	-11.1% (better)
macOS	BenchmarkChannelBuffered	20.410 ns/op	-26.4% (better)
macOS	BenchmarkChannelHandoff	6467 ns/op	-7.7% (better)
macOS	BenchmarkDefer	25.360 ns/op	-32.2% (better)
macOS	BenchmarkDirectCall	0.968 ns/op	-33.4% (better)
macOS	BenchmarkGlobalRead	1.030 ns/op	-14.9% (better)
macOS	BenchmarkGlobalWrite	0.943 ns/op	-36.6% (better)
macOS	BenchmarkGoroutine	28036 ns/op	-11.4% (better)
macOS	BenchmarkInterfaceCall	4.105 ns/op	-24.0% (better)
macOS	BenchmarkRuntimeGetG	2.066 ns/op	-19.8% (better)

Compared only with the latest matching platform in the main series.

Warning

• Persistent publishing is unavailable because no data token is configured.