fix(go): take a heap snapshot, not a 30-second delta

[mayankpande88]

Summary

Go heap profiles come back empty — the Profiler tab and any event evidence show a flamegraph with nothing in it:

Type: inuse_space
Duration: 30.02s, Total samples = 0
Showing nodes accounting for 0, 0% of 0 total

The request was /debug/pprof/heap?seconds=30. On the heap endpoint seconds does not mean "sample for this long" — Go samples, waits, samples again, and returns the difference. A service whose heap is steady across that window deltas to exactly zero.

A heap profile is a snapshot of what the process is holding, so it takes no duration. Dropping seconds and adding gc=1 — which collects first, so the snapshot describes live memory rather than whatever the last GC cycle left behind — turns the same request into a real profile.

Type of change

• Bug fix

Test plan

Reproduced against a real Go service with a steady ~64MB live heap and net/http/pprof, then confirmed the fix on the same process:

$ curl '/debug/pprof/heap?seconds=30'   # what we sent before
236 bytes
Duration: 30s, Total samples = 0
Showing nodes accounting for 0, 0% of 0 total

$ curl '/debug/pprof/heap?gc=1'         # what we send now
2247 bytes
Showing nodes accounting for 73.81MB, 100% of 73.81MB total
   71.81MB 97.28%  main.main
    1.50MB  2.04%  runtime.mallocgc
    0.50MB  0.68%  net/textproto.initCommonHeader

The empty output is character-for-character what the dev cluster produced: profiles of llm-server alternated between ~300 and ~16000 base64 bytes across four runs, the small ones decoding to a valid pprof with only sample-type headers and zero samples — i.e. whenever the heap happened to be steady for the 30s window.

go build ./... and go vet pass. Not unit-testable without an HTTP fixture: the URL is built inline in heapProfile and the function shells out to nsenter/wget.

Checklist

• go build ./... passes locally
• No breaking changes to the agent's stdout JSON envelope

Related issues

The last of the profiler defects from this series: #128 (image shipped no async-profiler), #129 (read-only rootfs / non-root targets), nudgebee/k8s-agent#619 (language detection).

[gemini-code-assist]

Code Review

This pull request updates the heap profiling URL in internal/agent/profiler/go_pprof.go to request a snapshot of live memory using ?gc=1 instead of a delta over a duration. Feedback suggests correcting the added comment to accurately describe Go's heap profiling behavior regarding garbage collection and to warn about potential latency spikes caused by forcing a garbage collection on large heaps.