tsk doctor is a one-shot health check against the active .tsk.md and tsk configuration. Designed for pre-commit hooks, CI gates, and fast triage when "something's weird."

Example

$ tsk doctor
file:    /Users/sanjay/tasks/.tsk.md
tz:      America/Los_Angeles
tasks:   142

all checks passed ✓

$ tsk doctor   # with a busted file
file:    /tmp/.tsk.md
tz:      Local
tasks:   3

ERRORS:
  ✗ unique_ids: id #1 appears on 2 tasks
exit 1

Checks

• file_present — .tsk.md exists and is readable
• file_parses — parses without error (error → exit 1)
• unique_ids — no duplicate IDs across tasks (error → exit 1)
• positive_ids — no negative IDs (error → exit 1)
• non_empty_title — no whitespace-only titles (warning)
• timestamp_sanity — completed >= created, due not 100+ years out (warning)
• timezone — reports active TSK_TZ/TZ/system default

Flags

• --json — machine-readable DoctorReport for scripts and CI

Exit Codes

• 0 — all checks passed (warnings don't flip exit code)
• 1 — at least one error
• 2 — bad invocation

New: SilentExitCoder

To avoid the noisy error: <msg> prefix on the legit failure path (doctor already prints its own report), this PR introduces a SilentExitCoder interface — an error that carries an exit code AND tells main.go to skip the default prefix. Doctor uses it for the "issues found" return path.

Cobra commands that need this pattern in the future can implement SilentExitCoder in their command file (the interface is exported, silentExit itself is package-private).

Tests

5 cases in doctor_test.go:

1. Clean store → "all checks passed"
2. --json emits parseable DoctorReport
3. Duplicate IDs → exit 1 + unique_ids error
4. Missing file → exit 1 + file_present error
5. SilentExitCoder shape: empty .Error(), code 1

All green with -race, gofmt-clean.

Part 4/10 of the v0.3.0 improvement series.