docs: enrich TODO.md with Phase 0 hardening tasks

Add Phase 0: ParseTranscript tests, ListSessions tests,
tool extraction coverage, parsing benchmarks.

Co-Authored-By: Virgil <virgil@lethean.io>

TODO.md

@@ -1,11 +1,23 @@
-# TODO.md -- go-session
+# TODO.md — go-session
+
+Dispatched from core/go orchestration. Pick up tasks in order.
+
+---
+
+## Phase 0: Hardening & Test Coverage
+
+- [ ] **Add parser tests** — Test `ParseTranscript()` with: minimal valid JSONL (1 user + 1 assistant message), tool call events (Bash, Read, Edit, Write, Grep, Glob, Task), truncated JSONL (incomplete last line), empty file, malformed JSON lines (should skip gracefully), very large session (1000+ events), nested tool results with arrays and maps.
+- [ ] **Add ListSessions tests** — Test with: empty directory, single session, multiple sessions sorted by date, non-.jsonl files ignored.
+- [ ] **Tool extraction coverage** — Test `extractToolInput()` for each supported tool type. Verify correct field extraction from JSON input.
+- [ ] **Benchmark parsing** — `BenchmarkParseTranscript` with a 10MB JSONL file. Measure memory and time.
+- [ ] **`go vet ./...` clean** — Fix any warnings.
 
 ## Phase 1: Parser Robustness
 
 - [ ] Handle truncated JSONL (incomplete final line, missing closing brace)
 - [ ] Handle very large sessions (streaming parse, avoid loading entire file into memory)
 - [ ] Handle non-standard tool formats (custom MCP tools, unknown tool names)
-- [ ] Add graceful error recovery -- skip malformed lines, log warnings
+- [ ] Add graceful error recovery — skip malformed lines, log warnings
 
 ## Phase 2: Analytics