workflow: Jira issue attachments (upload, list, download)

[studykit]

Summary

Add file-attachment support to the workflow plugin's issue surface when the
issue provider is Jira (Data Center): upload local files, see what is
attached after a fetch, and download attachments to local disk.

Jira-only throughout — GitHub issues have no equivalent REST surface, so the
verbs refuse any non-Jira provider and the issue-attach runbook intent is
injected into the LLM context only under Jira (GitHub/filesystem sessions
never learn the feature exists).

Capabilities

Upload

workflow issue attach add --issue <KEY> [--type <t>] <file>... — uploads
one or more local files in a single multipart request
(X-Atlassian-Token: no-check). Additive (no overwrite); refreshes the
issue cache afterward.

List (projection)

A fetch projects the issue's attachment list to a sibling attachment.md
(one line per attachment: - <id>: <filename> (<size> bytes)), written only
when the issue has attachments and surfaced in the fetch output alongside
relation.md. Deliberately kept out of issue.md body/frontmatter so the
authored content stays clean.

Download

workflow issue attach get --issue <KEY> (--id <ID>... | --name <FN>... | --all) [--out <dir>]
— resolves the chosen attachments against a live issue GET and downloads the
bytes (curl -L) to local disk so they can be opened/read. Defaults to the
issue cache dir's attachments/ subdir.

Flow: fetch → read ids from attachment.md → attach get --id <ID> → Read
the downloaded file.

Implementation

• Client: jira_upload_attachments (multipart) + jira_download_attachment
  (follow-redirect download); shared auth lines factored out.
• Provider: add_attachment (write) + get_attachment (read) operations;
  base raises not-implemented so GitHub inherits as unsupported.
• Projection: attachment.md normalize/render/write + read-only protection,
  surfaced via IssueFetchContext.attachments.
• Backend/CLI: attach subcommand group (add / get), Jira-only legacy
  guard.
• Hook injection: provider-keyed snippets/runbook/<provider>.md.
• Tests added across client/provider/cache/dispatcher/hook layers.
• Plugin version 0.6.3 → 0.7.1.