validation failed - RENAMED TO header collides with ADDED…

Error message

${specName} validation failed - RENAMED TO header collides with ADDED for "### Requirement: ${to}"

What it means

Validation inside buildUpdatedSpec: a RENAMED entry's TO header collides with a requirement in the ADDED section (same normalized name). Applying both would create two requirements with one name, so the delta set is rejected; at-fault input is the "### Requirement: <to>" header shared between a rename target and an addition.

Solutions

Remove the ADDED entry for that requirement since the rename already produces it
Rename the ADDED requirement or the RENAMED target to a different header

Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at src/core/specs-apply.ts:282 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Fission-AI/OpenSpec@6926ccb18a (2026-08-25). Data as JSON: /api/errors/91c0aa0fef5bfce6. Report an issue: GitHub.

Appendix: source

Thrown at src/core/specs-apply.ts:282

    // a case/whitespace variant cannot slip past the guard and degrade
    // into a warned no-op.
    const removedFoldMatch = [...removedNamesSet].find(
      (r) => foldRequirementName(r) === foldRequirementName(fromNorm)
    );
    if (removedFoldMatch !== undefined) {
      throw new Error(
        `${specName} validation failed - requirement present in multiple sections (RENAMED and REMOVED) for header "### Requirement: ${from}"` +
          (removedFoldMatch === fromNorm ? '' : ` (REMOVED spells it "${removedFoldMatch}")`)
      );
    }
    if (modifiedNames.has(fromNorm)) {
      throw new Error(
        `${specName} validation failed - when a rename exists, MODIFIED must reference the NEW header "### Requirement: ${to}"`
      );
    }
    // Detect ADDED colliding with a RENAMED TO
    if (addedNames.has(toNorm)) {
      throw new Error(
        `${specName} validation failed - RENAMED TO header collides with ADDED for "### Requirement: ${to}"`
      );
    }
  }
  if (conflicts.length > 0) {
    const c = conflicts[0];
    throw new Error(
      `${specName} validation failed - requirement present in multiple sections (${c.a} and ${c.b}) for header "### Requirement: ${c.name}"`
    );
  }
  const hasAnyDelta = plan.added.length + plan.modified.length + plan.removed.length + plan.renamed.length > 0;
  if (!hasAnyDelta) {
    throw new Error(
      `Delta parsing found no operations for ${update.id}. ` +
        `Provide ADDED/MODIFIED/REMOVED/RENAMED sections in change spec.`
    );
  }

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