yoloyolo/.planning/phases/06-config-package-and-sound-overrides/06-CONTEXT.md

Phase 6: Config Package and Sound Overrides - Context

Gathered: 2026-03-26 Status: Ready for planning

## Phase Boundary

Add a TOML-based configuration system that lets users override frequency and waveform per traffic class, with auto-discovery from standard paths, explicit --config flag, partial override semantics (only specified fields change), and strict unknown-key validation. Wire the merged config into the synthesis pipeline via the injection seam created in Phase 5.

Requirements covered: CFG-01 through CFG-05.

## Implementation Decisions

TOML Schema Design

• D-01: Use keyed TOML tables [sounds.<classname>] for per-class overrides. Each table supports frequency (float64, Hz) and waveform (string: "sine", "square", "sawtooth", "triangle"). Class names match classify.TrafficClass string values (e.g., [sounds.ICMP], [sounds.HTTPS]).
• D-02: Top-level structure is flat — no deeply nested hierarchies. Future phases (custom rules) will add [[rules]] array-of-tables at the top level.

Config Merge Semantics

• D-03: Per-field overlay merge — only fields explicitly set in TOML override defaults. Unspecified fields retain their built-in values. For example, setting only frequency for ICMP leaves its waveform and harmonics unchanged. This satisfies CFG-04 (partial override without replicating entire config).
• D-04: Merge produces a map[classify.TrafficClass]FreqConfig that is passed to synth.NewBank() via the injection seam from Phase 5. The default map is synth.ClassFreqConfigs.

Auto-Discovery and Precedence

• D-05: Discovery order (most-specific wins): --config <path> > ./netsynth.toml > ~/.config/netsynth/config.toml. If --config is specified and the file does not exist, exit with a clear error before capture begins (CFG-03). If no config is found via auto-discovery, proceed silently with defaults (CFG-02).
• D-06: Only one config file is loaded — no multi-file merge. The first found in precedence order wins entirely.

Validation and Error Reporting

• D-07: Unknown keys cause an immediate startup error naming the unrecognized key (CFG-05). Use TOML strict decoding to detect unknown keys. Suggest the closest valid key name if edit distance is small (nice-to-have, Claude's discretion on implementation).
• D-08: Type mismatches (e.g., frequency = "not a number") produce a clear error with field name and expected type, before capture begins.
• D-09: Unknown class names in [sounds.<classname>] produce a warning (not error) — this prepares for Phase 7 where user-defined class names are valid.

Pipeline Wiring

• D-10: encode.RunSynthesis signature changes to accept the merged config map (or loads config internally). The --config flag is added to the Cobra root command in cmd/netsynth/main.go.
• D-11: Config loading happens once at startup, before any capture begins — fail fast on all config errors.

Claude's Discretion

• TOML library choice (BurntSushi/toml vs pelletier/go-toml) — researcher should evaluate both
• Whether to create a dedicated config package or keep loading in cmd/netsynth
• Waveform string-to-WaveformType mapping implementation details
• Edit distance algorithm for typo suggestions (or skip if complexity isn't justified)

<canonical_refs>

Canonical References

Downstream agents MUST read these before planning or implementing.

Injection Seam (Phase 5 output)

• synth/bank.go — NewBank(tau float64, cfgs map[classify.TrafficClass]FreqConfig) — the injection point for merged config
• synth/config.go — ClassFreqConfigs default map, FreqConfig struct with WaveformType field, WaveformPresetHarmonics() function
• encode/mp3.go — RunSynthesis() calls synth.NewBank(1.0, synth.ClassFreqConfigs) — the call site to modify

CLI Entry Point

• cmd/netsynth/main.go — Cobra command setup, flag definitions, run() function that dispatches to live/pcap modes

Requirements

• .planning/REQUIREMENTS.md — CFG-01 through CFG-05 acceptance criteria

Prior Context

• .planning/phases/05-waveform-types-and-bank-decoupling/05-CONTEXT.md — Phase 5 decisions (D-02 WaveformType, D-05 bank injection seam)

No external specs — requirements fully captured in decisions above.

</canonical_refs>

<code_context>

Existing Code Insights

Reusable Assets

• synth.ClassFreqConfigs — Default config map (14 entries), serves as base for merge
• synth.WaveformType enum — Maps to TOML waveform strings (sine/square/sawtooth/triangle)
• synth.NewBank(tau, cfgs) — Already accepts injected config map (Phase 5)
• classify.TrafficClass (string type) — Keys for config map, matches TOML section names
• classify.AllClasses() — Returns all 14 built-in class names for validation

Established Patterns

• Cobra for CLI flags — add --config flag in same pattern as existing flags
• encode.RunSynthesis is the single call site for synthesis — modification point is narrow
• Package-level vars (ClassFreqConfigs, DefaultRules) serve as defaults — config system overlays on top

Integration Points

• cmd/netsynth/main.go:run() — Config loading inserts between flag parsing and capture start
• encode.RunSynthesis() — Must receive merged config map (currently hardcoded to synth.ClassFreqConfigs)
• synth.FreqConfig.WaveformType field — Set from TOML waveform string after parsing

</code_context>

## Specific Ideas

No specific requirements — standard TOML config pattern with partial merge semantics.

## Deferred Ideas

• --print-config command (CFG-06) — scoped to Phase 7
• Custom classification rules ([[rules]] TOML blocks) — scoped to Phase 7
• Config hot-reload — explicitly out of scope per REQUIREMENTS.md

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Phase: 06-config-package-and-sound-overrides Context gathered: 2026-03-26