bugfix - fix v0.3 release blockers (#542, #610, #612)

[dannymeijer]

Summary

This PR fixes the final v0.3 release-hardening blockers and follows up on the docs review. The compiler/tooling fixes keep incan test helper packaging, Rust interop call-shape metadata, stdlib runtime dependencies, and collection error paths aligned with the intended v0.3 behavior. The docs work splits oversized stdlib reference pages into Divio-shaped reference/how-to/explanation pages, restores legacy RFCs to the modern metadata shape, removes manually short-wrapped Markdown prose across project docs, and updates the generated language reference source so CI no longer rewrites generated prose back into short lines.

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• CI / tooling
• RFC (adds/updates docs/RFCs/*)

Area(s)

Select the primary areas touched (used for review routing; labels are managed separately):

• Incan Language (syntax/semantics)
• Compiler (frontend/backend/codegen)
• Tooling (CLI/formatter/test runner)
• Editor integration (LSP/VS Code extension)
• Runtime / Core crates (stdlib/core/derive)
• Documentation

Key details

• User-facing behavior: incan test includes the stdlib helper modules needed for lowered Result.map_err test code, and Rust interop no longer over-borrows by-value generic decode arguments when the selected method comes from an extension trait. Collection missing-key and invalid-count paths now raise the intended canonical key/value errors. The v0.3 docs are easier to reason about: release notes separate features from fixes, stdlib reference pages stay API-focused, and task/background material lives in how-to/explanation pages.
• Internals: the test module graph reuses the same implicit-helper surface detection as build/check/run; extension-trait Rust method metadata is validated into call-site parameter-shape facts; std.regex dependency ownership stays with source imports and registry metadata rather than the always-present runtime crate. The generated language-reference writer now emits natural Markdown paragraphs so the generated-reference CI guard agrees with the docs prose policy.
• Risks: this touches a wide docs surface, including RFC metadata/prose and generated reference output. Review should focus on accidental Markdown structure changes, especially tables, admonitions, and RFC metadata fields. The Rust interop call-shape change affects method calls where metadata is available; the fallback remains permissive when metadata is absent.

Testing / verification

• make test / cargo test
• make examples (if relevant)
• incan fmt --check . (if relevant)
• Manual verification described below

Manual verification notes:

• make -C /Users/danny/Development/encero/incan pre-commit passed after the final docs/generator commit: formatting, rustdoc coverage, 2438 nextest tests, 5 filtered cargo tests, clippy, cargo-deny, smoke-test-fast, examples checked 57 / ran 34 / failed 0, benchmark smoke builds checked 9 / failed 0.
• make -C workspaces/docs-site docs-build passed after the RFC frontmatter and stdlib docs split.
• cargo run -p incan_core --bin generate_lang_reference passed, and a shasum before/after idempotence check confirmed regenerated language.md and feature_inventory.md stay stable.
• Project Markdown short-prose scan over tracked and newly added *.md, excluding .agents, __research__, workspaces/docs-site/.venv, generated site output, and vendored license files, found 0 adjacent short-prose candidates.
• git diff --check passed.

Docs impact

• No docs changes needed
• Docs updated
• Docs follow Divio intent (tutorial/how-to/reference/explanation) where applicable

If docs updated:

• Link(s): workspaces/docs-site/docs/release_notes/0_3.md, workspaces/docs-site/docs/language/reference/stdlib/graph.md, workspaces/docs-site/docs/language/how-to/working_with_graphs.md, workspaces/docs-site/docs/language/explanation/graph_model.md, workspaces/docs-site/docs/language/how-to/hashing_data.md, workspaces/docs-site/docs/language/how-to/logging.md, workspaces/docs-site/docs/language/how-to/regular_expressions.md, plus broad Markdown prose unwraps across project docs.

RFC lifecycle note: this PR touches RFC Markdown for metadata modernization and prose reflow only; it does not implement or advance any active RFC lifecycle state.

Checklist

• I kept public docs user-focused and moved internals to contributing docs when appropriate
• I avoided duplicating canonical install/run instructions in multiple places
• I added/updated tests where it materially reduces regressions

Closes #542
Closes #610
Closes #612