docs(spike): SCIP overlay go/no-go for call graph (TAP-4096)#198
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Decision-support spike (not an ADR) evaluating an optional compiler-grade SCIP overlay that ingests an existing index.scip to upgrade ambiguous CALLS edges, with the deterministic AST/tree-sitter index as source of truth + fallback. Measured on the live tapps_mcp package (6,470 edges, 6,403 in-repo gaps): the 0.99 in-repo gap rate collapses to a ~58% SCIP-addressable ceiling (method calls) once builtins are excluded, and lower still after typed-receiver externals drop out. Verdict: NO-GO for now (no consumer emits index.scip; the staleness window is a new fabricate-an-edge liability; cheaper in-repo receiver typing is unspent) with a concrete GO trip-wire and a thin follow-up story outline. Holds ADR-0017 rejection / ADR-0026 deferral. Doc only, no code change. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Decision-support spike (not an ADR) for TAP-4096: evaluate an optional compiler-grade SCIP overlay that ingests an existing
index.scipwhen present to upgrade ambiguous CALLS edges, with the deterministic AST/tree-sitter index remaining source of truth + fallback. Doc only — no overlay implementation.Verdict: NO-GO for now (hold ADR-0017 rejection / ADR-0026 deferral)
Measured live on the
tapps_mcppackage viabuild_call_graph_index(6,470 edges, 6,403 in-repo gaps, 0.99 in-repo gap rate). Honest bucketing of the 10,241unresolved_static_callgaps:x.y()The headline 0.99 rate overstates the win ~3×: the classifier's
expr_rootheuristic counts builtins/local-method calls as in-repo. Genuine SCIP-addressable ceiling ≈58%, realistic in-repo gain ≈20-35% after typed-receiver externals drop out.Why NO-GO: (1) win is real but modest; (2) no consumer emits
index.sciptoday, so the "near-zero marginal cost" premise has no live input; (3) a stale.scipcan draw a wrong edge — the ADR-0004 fabricate-an-edge failure mode; (4) cheaper deterministic in-repo receiver typing (ADR-0026receiver_untyped/ TAP-4540 lineage) captures a chunk of the same edges with no external toolchain. Includes a concrete GO trip-wire + thin S1-S4 follow-up outline if a consumer starts shippingindex.scip.Where it would plug in (verified anchors)
call_graph.py:306-311(full-build_finalize_index) +call_graph.py:322-366(incrementalupdate_call_graph_index, byte-equivalence invariant)call_graph_fingerprint.py:149-159compute_index_fingerprint(fold.sciphash for staleness)INDEX_VERSION5 → 6 bump;call_graph_cache.py:351-386migration pathTest
Docs-only, no Python touched. Markdown well-formed, all internal file/ADR refs verified to exist; ADR-0017/0026 line anchors confirmed. No docs index lists spikes (repo convention), so no index change.
🤖 Generated with Claude Code