fix: config warnings honor logging.format/level (#113)

[skyoo2003]

Summary

Config-time log warnings emitted during config.parse() now honor the operator-configured logging.format/logging.level instead of always going out through the default text handler before logging was set up.

Related Issue

Fixes #113

Changes

• Add cmd/devcloud/buffer.go: a buffering slog.Handler that captures records and replays them through a destination handler, gated by that handler's level filter (flushTo).
• Wire it into cmd/devcloud/main.go: install the buffer as the default handler before config load, then replay buffered records through the real handler after setupLogging(). The load-error path falls back to the default handler and flushes so the error and any buffered warnings are still surfaced.
• internal/config is left untouched — the fix is purely a startup-ordering change in main.
• Add a Fixed changelog fragment.

Test Plan

• New cmd/devcloud/buffer_test.go: buffered Info+Warn records flushed to a JSON handler at level=warn — asserts the Warn record (with structured attrs) is replayed as JSON and the Info record is dropped; a second flush is a no-op. Also asserts the buffer accepts all levels.
• go vet ./cmd/devcloud/, go test ./cmd/devcloud/, go build ./... all pass.
• golangci-lint run ./cmd/devcloud/ → 0 issues.
• Manual end-to-end: DEVCLOUD_SERVICES=tier9 devcloud --config <yaml with logging.format=json, deprecated dashboard key> → both config warnings now emit as JSON with structured attrs ("token":"tier9").

Checklist

• Self-reviewed the code
• Added/updated tests
• Lint/format passes (golangci-lint run)
• Updated documentation (if applicable) — N/A
• Added a Changie changelog fragment for user-facing changes (changie new, see docs/release.md)

[sourcery-ai]

Reviewer's Guide

Startup logging is refactored so config-time warnings are first buffered via a temporary slog.Handler and then replayed through the operator-configured logger, ensuring they honor logging.format/logging.level; tests validate buffering and flushing behavior, and a changelog fragment documents the fix.

File-Level Changes

Change	Details	Files
Introduce a buffering slog handler used during startup to capture pre-config logging output and later replay it through the real handler, honoring its format and level.	Implement bufferHandler that stores cloned slog.Record values and exposes Enabled, Handle, WithAttrs, WithGroup, and flushTo methods. Ensure flushTo replays only records accepted by the destination handler’s level filter and then clears the buffer. Document single-threaded assumptions in bufferHandler with a note about adding a mutex if startup logging becomes concurrent.	cmd/devcloud/buffer.go
Wire the buffer handler into the devcloud startup flow so config.parse() warnings are emitted through the configured logger or the default handler on failure.	Install bufferHandler as the default slog handler before config loading begins. On config load failure, initialize logging with an empty LoggingConfig, flush buffered records to the resulting default handler, then log and exit on error. On successful config load, call setupLogging with cfg.Logging and flush buffered records to the now-configured default handler.	cmd/devcloud/main.go
Add tests that verify buffered records respect the destination handler’s JSON formatting and level filtering when flushed.	Test that buffered Info and Warn records flushed to a JSON handler at level=warn result in only the Warn record being emitted as JSON with structured attributes, and that a second flush is a no-op. Test that bufferHandler.Enabled returns true for debug level to confirm it buffers all levels without pre-filtering.	cmd/devcloud/buffer_test.go
Document the user-facing behavior change that config-time warnings now honor logging.format/logging.level.	Add a changelog fragment describing that config-time warnings (deprecated dashboard key, unknown tier) now use the configured logging format and level. Associate the changelog fragment with issue config: warnings in parse() emit before logging is configured (ignores logging.format/level) #113 via a custom Issue field.	.changes/unreleased/Fixed-113.yaml

Possibly linked issues

• config: warnings in parse() emit before logging is configured (ignores logging.format/level) #113: PR adds a buffering slog handler and startup changes so config-time warnings emit using configured format/level.

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[sourcery-ai]

Hey - I've left some high level feedback:

• The bufferHandler is explicitly single-threaded; if there’s any chance config-loading logs could be emitted from multiple goroutines in the future, consider adding a mutex now to avoid subtle data races around the records slice.
• bufferHandler.WithAttrs and WithGroup intentionally no-op, which could be surprising if future config-time logging starts using structured logging; consider tracking attrs/groups so the behavior matches other handlers even during buffering.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The bufferHandler is explicitly single-threaded; if there’s any chance config-loading logs could be emitted from multiple goroutines in the future, consider adding a mutex now to avoid subtle data races around the records slice.
- bufferHandler.WithAttrs and WithGroup intentionally no-op, which could be surprising if future config-time logging starts using structured logging; consider tracking attrs/groups so the behavior matches other handlers even during buffering.

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