implementation-coverage

# Implementation Coverage Own profile semantics, exact coverage policy, selected-Go cover invocation, and optional local source comparisons. Let the report package own visual presentation and the app own final status precedence. ## Select the coverage operation - Read [profiles and thresholds](references/profiles-and-thresholds.md) for grammar, bounded parsing, merging, weighted totals, or minimum policy. - Read [canonical HTML](references/canonical-html.md) for raw profile handling, Go cover invocation, secure decoration, publication, or cleanup. - Read [explicit source baselines](references/source-diff.md) for revision resolution, source mapping, bounded edit models, or Git failure behavior. Inspect the linked implementation and tests for each affected operation. Inputs are raw profiles, selected workdir/toolchain, optional exact decimal policy, and an explicitly requested revision. Outputs are deterministic weighted models, a recomputable policy decision, and applicable coverage artifacts. ## Keep evidence and policy distinct Preserve raw profile bytes and source-path identities. Calculate integer covered/total statement weights, never a mean of percentages. Keep disabled, missing, empty, malformed, and genuinely zero-covered profiles distinct. Evaluate policy only against valid available coverage. Equality satisfies the exact threshold; display rounding never decides status. Keep a coherent below-minimum result (exit 3) distinct from unavailable policy evidence (exit 2) and preserve stronger child failure or cancellation. Generate annotated HTML with the selected Go tool from the project workdir. Preserve its source, spans, selector, and script; allow only the report-owned, exactly removable head injection. Stage securely and retain raw evidence when parsing, cover execution, decoration, or publication fails. Resolve a baseline only when explicitly requested, once to an immutable local commit. Bound every comparison dimension and fail visibly on missing objects or ambiguous mappings. Without a baseline, neither invoke Git nor imply source changes. Keep old and current source sensitive and unredacted. ## Verification and acceptance Use focused profile/threshold tests for mathematical and grammar behavior, real-toolchain cover tests for canonical bytes, local Git fixtures for source comparison, and app tests for status and artifact coherence. Browser behavior requires separate report verification; a valid comparison model alone does not qualify an interactive explorer. - Unequal file weights produce the aggregate weighted ratio, not the mean of their percentages. - Duplicate `set` blocks merge as covered if any count is nonzero. - Duplicate `count` or `atomic` blocks add counts without adding statement weight twice. - Mixed modes, conflicting weights, invalid coordinates, and count overflow fail explicitly. - A colon-bearing source path and a very large valid line parse correctly. - Go-emitted zero-statement regions parse and merge without changing totals. - Disabled, missing, empty, malformed, zero-covered, and partial coverage remain distinguishable in summaries and exit policy. - An exactly representable threshold equal to the weighted ratio passes; finite decimals on either side of a repeating ratio compare correctly. Uint64-scale counts never overflow or pass through binary floating point. - `go tool cover` resolves relative source paths from the project workdir and never publishes failed partial HTML. - The fixed decorator is byte-deterministic across chunk boundaries, accepts the selected Go toolchain's document, rejects malformed or already-decorated heads, contains no external resources, and is exactly reversible by removing its exact rendered injection. - A real selected-toolchain integration retains the `#files` selector, `pre.file` source panels, coverage spans, and change script after decoration. - An explicit baseline resolves to one commit, includes only unambiguously matched current-profile files, renders deterministic added/modified/renamed edit scripts, and fails clearly for missing Git objects, malformed output, ambiguity, cancellation, and every configured bound. - Without `--coverage-diff-base`, Git is never invoked and the report exposes coverage focus without fabricating source changes or a split comparison.