diff --git a/.planning/phases/06-config-package-and-sound-overrides/06-CONTEXT.md b/.planning/phases/06-config-package-and-sound-overrides/06-CONTEXT.md
new file mode 100644
index 0000000..5d19f77
--- /dev/null
+++ b/.planning/phases/06-config-package-and-sound-overrides/06-CONTEXT.md
@@ -0,0 +1,111 @@
+# Phase 6: Config Package and Sound Overrides - Context
+
+**Gathered:** 2026-03-26
+**Status:** Ready for planning
+
+<domain>
+## 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.
+
+</domain>
+
+<decisions>
+## 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)
+
+</decisions>
+
+<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>
+
+<specifics>
+## Specific Ideas
+
+No specific requirements — standard TOML config pattern with partial merge semantics.
+
+</specifics>
+
+<deferred>
+## 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
+
+</deferred>
+
+---
+
+*Phase: 06-config-package-and-sound-overrides*
+*Context gathered: 2026-03-26*
diff --git a/.planning/phases/06-config-package-and-sound-overrides/06-DISCUSSION-LOG.md b/.planning/phases/06-config-package-and-sound-overrides/06-DISCUSSION-LOG.md
new file mode 100644
index 0000000..582233d
--- /dev/null
+++ b/.planning/phases/06-config-package-and-sound-overrides/06-DISCUSSION-LOG.md
@@ -0,0 +1,75 @@
+# Phase 6: Config Package and Sound Overrides - Discussion Log
+
+> **Audit trail only.** Do not use as input to planning, research, or execution agents.
+> Decisions are captured in CONTEXT.md — this log preserves the alternatives considered.
+
+**Date:** 2026-03-26
+**Phase:** 06-config-package-and-sound-overrides
+**Areas discussed:** TOML structure, Config merge, Auto-discovery precedence, Error reporting
+**Mode:** --auto (all areas auto-selected, recommended defaults chosen)
+
+---
+
+## TOML Structure
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Keyed table `[sounds.<classname>]` | Natural TOML pattern, matches traffic class names | ✓ |
+| Flat key-value pairs | Simpler but doesn't scale to per-class overrides | |
+| Nested `[sounds.<classname>.audio]` | Unnecessary nesting depth | |
+
+**User's choice:** [auto] Keyed table `[sounds.<classname>]` (recommended default)
+**Notes:** Matches classify.TrafficClass string values directly. Supports `frequency` and `waveform` fields per class.
+
+---
+
+## Config Merge Semantics
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Per-field overlay | Only specified fields override defaults (CFG-04) | ✓ |
+| Full section replace | Setting any field in a class replaces all fields | |
+| Deep merge with arrays | Overkill for flat config structure | |
+
+**User's choice:** [auto] Per-field overlay (recommended default)
+**Notes:** Satisfies CFG-04 requirement. User sets one field, everything else keeps defaults.
+
+---
+
+## Auto-Discovery Precedence
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Local > user > flag | Most-specific wins: --config > ./netsynth.toml > ~/.config/ | ✓ |
+| Flag only | Simpler but no auto-discovery (violates CFG-02) | |
+| Multi-file merge | Load and merge all found configs | |
+
+**User's choice:** [auto] Local > user-level > flag (recommended default)
+**Notes:** Standard CLI convention. Only one file loaded — no multi-file merge complexity.
+
+---
+
+## Error Reporting
+
+| Option | Description | Selected |
+|--------|-------------|----------|
+| Fail-fast with key name + suggestion | Exit at startup, name the bad key (CFG-05) | ✓ |
+| Warning and continue | Tolerant but hides mistakes | |
+| Strict with no suggestions | Simpler but less helpful | |
+
+**User's choice:** [auto] Fail-fast with key name and optional typo suggestion (recommended default)
+**Notes:** Matches CFG-05 requirement. Unknown class names are warnings (not errors) to prepare for Phase 7.
+
+---
+
+## Claude's Discretion
+
+- TOML library choice
+- Package organization (dedicated `config` package vs inline)
+- Waveform string mapping implementation
+- Edit distance for typo suggestions
+
+## Deferred Ideas
+
+- `--print-config` (CFG-06) — Phase 7
+- Custom rules `[[rules]]` — Phase 7