0539 — Blank-line convention for function bodies

Context

14b’s internal file-structure cleanup called for a rule on when a statement gets a blank line before/after it. Sampling RegisterTopic, the datastore’s registerTopic, and messageRunner.prefetch showed the codebase already follows one consistent shape — the rule needed naming, not inventing.

Decision

A Blank lines section in CONVENTIONS.md: function bodies read as paragraphs — one blank line between steps, none inside a step.

• A step is the group of statements one comment could name; groups you would caption separately get a blank line between them.
• Glue rules (mechanical): never a blank line between a statement and what consumes its result — the err check, a nil/comma-ok branch on the returned value, the defer that releases what it acquired, the Exec/QueryRow running a SQL literal declared above it.
• A mid-body comment binds downward: blank before it, never between it and its statement.
• A validation preamble is one step: guards glued, one blank after the last.
• At most one consecutive blank inside a body; none directly after { or before }.

Enforcement is the full paragraph rule (user-settled option A), not just the mechanical glue subset — the sweep judges step boundaries in every function body.

Consequences

• The sweep runs rule-by-rule project-wide (user-settled), shared with the file-layout sweep ([0538]): one pass per rule across the main module, mechanical rules first, the paragraph-step judgment pass last.
• The comment-binds-downward bullet restates the existing Comments rule (“rationale directly above the statement it explains”) from the whitespace side; the two must stay consistent.