When a user types (or has) a Title that already exists — either among other files in the current stash session or among the user's own previously published Commons files — offer to convert the colliding titles into a numbered sequence using a # placeholder. The user accepts the suggestion, and the tool resolves the actual numbers at publish time, continuing whatever sequence the user already owns.

Trigger:

• Not driven by the user typing # themselves.
• Driven by collision detection when a Title equals:
  • Another row's Title in the current stash (multiple files share the same base name), or
  • A Commons file that the current user previously published.
• Detection happens during editing; the actual number assignment happens at publish time.

Suggestion behavior:

• When a collision is detected, an inline suggestion appears: "Convert to sequence — add #".
• Accepting the suggestion rewrites the Title of all stash rows sharing that base name to <basename> #.
• The # is a placeholder that resolves to a concrete integer at publish time.

Publish-time resolution:

• The tool queries Commons for the user's existing <basename> N files (own files only) and finds the highest N already used.
• Each <basename> # in the stash is published as <basename> N+1, <basename> N+2, … continuing the sequence.
• If no prior owned sequence exists, numbering starts at 1.
• Sequence length is unbounded — detection doesn't care how long the existing sequence is.

When NOT to offer the suggestion:

• If the base name is already used by someone else on Commons, do not offer the sequence suggestion. The user has to resolve the collision via standard title validation (covered by T425880).
• "Used by someone else" = any file with that base name where the uploader is not the current user.

Out of scope:

• Manually-typed # as a user-facing variable (this is suggestion-driven only).
• Generic template variables — handled by T425887 (advanced title and description generation). This task and T425887 are related but standalone: T425887 is about user-authored templates with variables; this task is about a single, opinionated auto-suggestion for the sequence pattern.
• Auto-suggesting alternate base names when the name is taken by someone else (intentionally not offered).

Acceptance:

• Typing a Title that matches another stash row or one of the user's own published files surfaces the "Convert to sequence" suggestion.
• Accepting rewrites all matching stash rows to <basename> #.
• At publish time, the # placeholders resolve to consecutive integers continuing from the highest owned <basename> N on Commons (or starting at 1).
• Suggestion does not appear when the base name is in use by another user.

Related: T425880 (title validation), T425887 (template-based title/description generation).

Source: User feedback session.