feat(2b): config hardening — .env, password_file, SIGHUP + rename-safe watcher

[fjacquet]

Phase 2b — Config Hardening

Adds .env loading, file-backed secrets, and robust reload triggers without changing any metric output. Implements all of Phase 2 spec §2b (plan).

What's in it

• .env loading (5f922fc) — config.LoadDotEnv runs before ${VAR} interpolation so config references resolve. Uses joho/godotenv, which never overrides already-set env vars (real secret injection always wins).
• password_file secrets (c2077de) — per-host/auths password_file: read at validate time and trimmed; wins over inline password. Re-read on every reload, so secret rotation is picked up without a restart.
• SIGHUP + rename-safe watcher (488f965) — kill -HUP triggers a reload; the fsnotify watcher now handles Rename/Remove (editor atomic-save) with a bounded re-add. Deliberately avoids upstream PR Improve config file watcher resilience mrlhansen/idrac_exporter#148's goroutine-leaking recursion and per-event sleep.

Contract-neutrality

internal/collector is byte-for-byte unchanged — metric output is unaffected. go.mod adds only github.com/joho/godotenv v1.5.1 (no errgroup/resty/OTLP scope creep).

Verification

• gofmt -l . clean, go vet ./... clean
• go test -race ./... → 9 pass across 5 packages
• golangci-lint run ./... → 0 issues
• govulncheck ./... → no vulnerabilities

Known follow-ups (pre-existing, out of scope)

• The 1s dedup gate runs before the rename/remove re-add — an editor atomic-save (write→rename <1s later) can silently drop the watch. Identical at base; inherited, not introduced.
• Reader-writer race on config.Config.Collect/.Event read without Config.Mutex in internal/collector — wants a Config.Snapshot() accessor.

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ba2c1419-0b9f-4e7d-bd5b-46c904f6bf17

📥 Commits

Reviewing files that changed from the base of the PR and between f0b9ebc and 488f965.

⛔ Files ignored due to path filters (1)

• go.sum is excluded by !**/*.sum

📒 Files selected for processing (11)

• cmd/idrac_exporter/config.go
• cmd/idrac_exporter/config_test.go
• cmd/idrac_exporter/main.go
• cmd/idrac_exporter/signals.go
• docs/superpowers/plans/2026-06-15-phase2b-config-hardening.md
• go.mod
• internal/config/config.go
• internal/config/config_test.go
• internal/config/dotenv.go
• internal/config/dotenv_test.go
• internal/config/model.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch phase2b-config

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