Mux

coder/mux — Coder's desktop/CLI app for parallel agentic development. Mux makes its own LLM API calls (via the Vercel AI SDK) and records per-turn token usage natively, so codeburn reads it directly.

• Source: src/providers/mux.ts
• Loading: eager (src/providers/index.ts:13)
• Test: tests/providers/mux.test.ts

Where it reads from

Order	Path
1	$CODEBURN_MUX_DIR (codeburn-only override)
2	$MUX_ROOT (mux's own override)
3	~/.mux (default)

Session files: <root>/sessions/<workspaceId>/chat.jsonl, plus each spawned sub-agent's own transcript at <root>/sessions/<workspaceId>/subagent-transcripts/<childTaskId>/chat.jsonl (see Quirks). Dev builds of mux use ~/.mux-dev and an older install may use ~/.cmux (migrated to ~/.mux); point CODEBURN_MUX_DIR/MUX_ROOT at those if needed.

The human-readable project name is resolved from <root>/config.json (shape: { projects: Array<[projectPath, { workspaces: [{ id }] }] > }); the directory under sessions/ is the workspaceId, matched against workspace.id. Falls back to the raw workspaceId when there's no mapping.

Storage format

JSONL, one MuxMessage per line. Token usage rides on each assistant message's metadata.usage ({ inputTokens, outputTokens, reasoningTokens, cachedInputTokens }, typed z.any() upstream so it's read defensively). Tool calls and the user prompt are parts[] entries (dynamic-tool / text).

Pricing

Cost is recomputed locally via calculateCost (mux and codeburn both price from the LiteLLM snapshot). On-disk model strings are provider:modelId (e.g. anthropic:claude-opus-4-8); the provider: prefix is stripped at parse time so the stored model is the bare LiteLLM id. This matters because codeburn's canonicalizer (getCanonicalName) only strips slash-style prefixes, and parser.ts re-prices from the stored model after the cache round-trip — a colon-prefixed model would price at $0 and render raw in the breakdown.

Token decomposition matches mux's own displayUsage.ts (AI SDK v6 semantics):

• inputTokens is inclusive of cache-read and cache-creation → input = inputTokens − cachedInputTokens − cacheCreation.
• outputTokens is inclusive of reasoning → output = outputTokens − reasoning; reasoning bills at the output rate, so it's folded back into the output arg of calculateCost.
• Cache-creation tokens are provider-specific: read from metadata.providerMetadata.anthropic.cacheCreationInputTokens.

Caching

None at the provider level.

Deduplication

Per mux:<workspaceId>:<message.id>. message.id is required by mux's schema; for corrupt id-less lines it falls back to the (unique) line index.

Quirks

• No double-counting with claude. Mux calls model APIs itself and stores usage under ~/.mux; it does not shell out to Claude Code or read ~/.claude.
• Sub-agents. A spawned sub-agent is its own LLM-client session, but mux writes it to sessions/<workspaceId>/subagent-transcripts/<childTaskId>/chat.jsonl — nested under the parent workspace, not as a top-level sessions/<id> dir. discoverSessions walks these explicitly and attributes them to the parent's project; missing them undercounts real sessions substantially (sub-agent calls are routinely the majority of a session's turns). No double-count: the dedup key is derived from the <childTaskId> directory name, which is disjoint from every workspace id.
• Reasoning vs. output decomposition. output = outputTokens − reasoningTokens assumes outputTokens is reasoning-inclusive, which holds for every record carrying outputTokenDetails (text + reasoning). A small fraction of Google gemini-3-*-preview records report reasoningTokens > outputTokens; for those the text component clamps to 0 (reasoning is still billed at the output rate). This matches mux's own displayUsage.ts and the token/cost effect is negligible.
• Read only chat.jsonl. session-usage.json (pre-aggregated per model) and analytics/analytics.db (DuckDB, derived from chat.jsonl) describe the same usage; summing them would double-count.
• No web-search field. Mux records no web-search/server-tool request count, so webSearchRequests is always 0.
• Remote runtimes. Mux can run workspaces on SSH/Docker, but the desktop app is the LLM client and writes sessions/*/chat.jsonl on the machine running mux — so usage is captured locally regardless of where commands execute.

When fixing a bug here

1. Confirm whether the bug is in discovery (sessions not picked up — discoverSessions/loadProjectMap) or parsing (createParser).
2. metadata.usage is untyped upstream and its exact field set varies by provider family (anthropic/openai/google/xai/deepseek). Validate against a real chat.jsonl sample and cross-check the parsed per-model totals against the sibling session-usage.json byModel — they should match.
3. Add a fixture-driven case to tests/providers/mux.test.ts. Do not mock the filesystem; write a temp ~/.mux layout like the existing tests.