Differentiation Matrix for Portfolio-Aligned Textbook Series: FS2P Vol 3–4 vs Python Pathway Vol 3–4

Two textbook series within the same program — From Scratch to Python (FS2P) and Python Pathway (PP, proposed under ADR-003) — share the canonical K-12 algorithmic topic surface at Vol 3 (data structures / core algorithms) and Vol 4 (competitive content). The overlap is structurally unavoidable: any K-12 curriculum with an HSG Tin endpoint crosses the same VOI / IOI syllabus canon. ADR-003 §2.6 commits PP to independence from FS2P at a deeper level — pedagogy, narrative, framing, example-set — rather than language or chapter ordering. This paper operationalises that commitment by (a) reviewing textbook-differentiation case studies from the algorithmic canon (Sedgewick / CLRS / Knuth) and the CP canon (Halim / Skiena / Laaksonen) with Ries-Trout positioning and Christensen jobs-to-be-done framing, (b) constructing a chapter-level differentiation matrix on four dimensions for FS2P Vol 3–4 (scanned from the 2026-04-19 build, 341 pages) vs PP Vol 3–4 (proposal per structure document), (c) scoring cannibalization risk into high- / moderate- / low-risk zones and deriving mitigation rules for high-risk cells, and (d) producing an authoring style-guide clause package enforcing the divergence at design time. The contribution is strategic, not novel-pedagogy: a design artefact that unblocks PP Vol 3–4 drafting and converts ADR-003 §2.6 into a verifiable commitment. Target is the auditloop rigor bar, not venue submission.