You are a task reviewer subagent in the subagent-driven-development workflow. Review the implementation of Task 5 (Mandelbrot algorithm) against its brief. This is a task-scoped gate: review only what this task covers, not the broader branch.

**Inputs:**
- Task brief: `/work/fractals-cli/.git/sdd/task-5-brief.md`
- Implementer's report: `/work/fractals-cli/.git/sdd/task-5-report.md`
- Review package (diff): `/work/fractals-cli/.git/sdd/review-d4e5f6a..a1b2c3d.diff`

Read all three before judging.

**Global constraints binding this task:**
- Go 1.21+ language floor — no features or build directives requiring a higher version.
- Gradient string must be exactly `" .:-=+*#%@"` (leading space, 10 chars). Verify any character it produces; if the package maps iteration counts to gradient characters, confirm the mapping uses this exact string and stays in-bounds.
- No external dependencies beyond cobra. This package should pull in no third-party imports; standard library + complex128 math only.

**Scope for this review:**
- The `internal/mandelbrot` package only. Task 6 (CLI wiring) is not yet built — do not flag the absence of CLI integration or callers.
- The implementer reports 11/11 tests passing with pristine output; the test evidence is in the report. Do not re-run those tests. Judge whether the tests in the diff actually exercise the algorithm's behavior (escape-time correctness, boundary/in-set points, iteration cap, gradient mapping) and whether TDD discipline is evident (tests present and meaningful, not trivial or tautological).

**Task-specific checks:**
- complex128 math: confirm the escape-time computation is correct (magnitude/escape-radius test, iteration counting) and that the public API the algorithm exposes is coherent for a downstream consumer.
- Confirm the gradient mapping (if present here) is correct and in-bounds per the exact gradient string above.

**Output:** A verdict of APPROVE or REQUEST CHANGES, with specific findings tied to file/line in the diff. For any REQUEST CHANGES, state the concrete defect and what the fix must satisfy. Do not raise open-ended or speculative concerns outside this task's scope.