[FEATURE] Add --from-issue, like --from-pr but for issues

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

--from-pr lets you resume a session linked to a PR. I want the same thing for issues.

The scenario I keep hitting: I grab an issue, spend an hour or two with Claude poking around the code and talking through the fix, then I get pulled into something else and close the session. Two days later I come back and all of that context is gone. I'm re-reading the issue, running the same greps I ran before, and re-explaining the approach I already worked out with Claude last time.

--from-pr solves exactly this, just later in the cycle — after the PR exists. The same problem exists at the issue stage, but there's no equivalent flag for it.

I checked claude --help and the CLI reference. --from-issue doesn't exist right now.

Proposed Solution

I'd like this to mirror --from-pr as closely as possible: no new "start" flag, just a resume flag.

claude --from-issue 123
claude --from-issue https://github.com/org/repo/issues/123

The session should auto-link to an issue during normal use, for example when gh issue view <n> gets run in the session, or when a commit message contains fixes #123 / closes #456. That's the same auto-linking pattern --from-pr already uses with gh pr create.

Unlike PRs, one issue can span multiple sessions over days or weeks. If --from-issue finds more than one linked session, it should open a picker like /resume does.

Alternative Solutions

I've been working around this a few ways, none of them great:

• claude --resume with the picker. Works, but I have to remember or search for the session name. There's no semantic connection between the session and the issue I was working on.
• Naming sessions manually (e.g., issue-789). Depends entirely on me being disciplined about it, and I forget half the time.
• A custom slash command like /fix-issue 1234. Can fetch the issue content, but starts from scratch every time. No memory of previous investigation.

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Example scenario:

1. I pick up an auth timeout bug and spend an hour in a Claude session digging through the code. We find the root cause and agree on a fix.
2. I get pulled into a meeting and close the session before writing any code.
3. Two days later I run claude --from-issue https://github.com/org/repo/issues/789 and Monday's context is back: investigation, files, the plan we landed on.
4. I implement the fix right away instead of re-reading the issue, re-running the same greps, and re-explaining the approach to Claude.

Additional Context

#10998 (open) is about Claude Code being able to fetch GitHub issue content directly. That's a different feature — it helps when you're starting work on an issue. This request is about resuming a session that's already been working on one.

#23296 (closed) proposed claude --work-on "#346", which combined worktree creation, issue fetching, and session naming. It was closed without implementation. This request is just the session-linking piece, matched to the existing --from-pr shape.

#22303 (closed) asked for the same --from-pr parity but for GitLab merge requests. I'm scoping this one to GitHub issues.