feat: code agent post-script and provider

.fullsend/harness/code.yaml

@@ -0,0 +1,12 @@
+agent: agents/code.md
+image: quay.io/manonru/fullsend-exp:latest
+policy: policies/code.yaml
+
+providers:
+  - github
+
+post_script: scripts/post-code.sh
+
+runner_env:
+  ISSUE_NUMBER: "${ISSUE_NUMBER}"
+  REPO_FULL_NAME: "${REPO_FULL_NAME}"

.fullsend/providers/github.yaml

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+name: github
+type: generic
+credentials:
+  GH_TOKEN: "${FULLSEND_CODE_BOT_TOKEN}"

.fullsend/scripts/post-code.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+# Contract: repo extraction (run.go) places the modified repo here
+# before the sandbox is deleted.
+REPO_DIR="repo"
+
+if [ ! -d "${REPO_DIR}" ]; then
+  echo "error: extracted repo not found at ${REPO_DIR}" >&2
+  exit 1
+fi
+
+cd "${REPO_DIR}"
+
+BRANCH="$(git branch --show-current)"
+
+if [ -z "${BRANCH}" ] || [ "${BRANCH}" = "main" ] || [ "${BRANCH}" = "master" ]; then
+  echo "error: agent did not create a feature branch" >&2
+  exit 1
+fi
+
+# Rewrite remote to use the GitHub App token for push auth.
+git remote set-url origin \
+  "https://x-access-token:${GH_TOKEN}@github.com/${REPO_FULL_NAME}.git"
+
+git push -u origin "${BRANCH}"
+
+# Create PR linking to the originating issue.
+gh pr create \
+  --repo "${REPO_FULL_NAME}" \
+  --head "${BRANCH}" \
+  --title "fix: resolve #${ISSUE_NUMBER}" \
+  --body "Closes #${ISSUE_NUMBER}"

docs/superpowers/specs/2026-04-15-code-agent-post-script-design.md

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+# Code Agent Post-Script and Provider
+
+Date: 2026-04-15
+
+## Problem
+
+The code agent runs inside an OpenShell sandbox, reads an issue, implements a
+fix, and commits to a feature branch. When the sandbox is destroyed, the commit
+is lost. The automation layer that turns the agent's local commit into a pushed
+branch and PR does not exist yet.
+
+This is the post-script component of the code agent harness -- the credentialed
+write-back step described in [ADR-0017][adr-0017]. It runs on the host after
+sandbox cleanup, outside the agent's isolation boundary.
+
+## Dependencies
+
+- **Repo extraction** (Marta): Modified repo must be extracted from the sandbox
+  into `runDir/repo/` before teardown. The post-script assumes this contract.
+- **PR #231** (`fullsend run` CLI): The `Harness` struct and `run.go` execution
+  flow already support `post_script`, `providers`, and `runner_env` fields. This
+  work produces configuration that plugs into that machinery.
+- **`code.yml` workflow**: Must export `ISSUE_NUMBER` and `REPO_FULL_NAME` as
+  environment variables before calling `fullsend run`.
+
+## Design
+
+### File layout
+
+```
+.fullsend/
+  harness/code.yaml          # harness definition for the code agent
+  providers/github.yaml      # GH_TOKEN provider
+  scripts/post-code.sh       # post-script: push branch + open PR
+```
+
+### Provider: `.fullsend/providers/github.yaml`
+
+```yaml
+name: github
+type: generic
+credentials:
+  GH_TOKEN: "${FULLSEND_CODE_BOT_TOKEN}"
+```
+
+Maps the workflow-level `FULLSEND_CODE_BOT_TOKEN` (set by `setup-agent-env.sh`
+after prefix-stripping) to `GH_TOKEN` for the post-script. The token is
+available only on the host side; it never enters the sandbox (per ADR-0017).
+
+### Harness: `.fullsend/harness/code.yaml`
+
+```yaml
+agent: agents/code.md
+image: quay.io/manonru/fullsend-exp:latest
+policy: policies/code.yaml
+
+providers:
+  - github
+
+post_script: scripts/post-code.sh
+
+runner_env:
+  ISSUE_NUMBER: "${ISSUE_NUMBER}"
+  REPO_FULL_NAME: "${REPO_FULL_NAME}"
+```
+
+- `agents/code.md` and `policies/code.yaml` are out of scope; the harness
+  references them for completeness.
+- `ISSUE_NUMBER` and `REPO_FULL_NAME` originate from the dispatch workflow's
+  GitHub event payload. The workflow must export them before calling
+  `fullsend run`.
+- No `pre_script`, `skills`, `host_files`, or `validation_loop` -- those can be
+  added as the code agent matures.
+
+### Post-script: `.fullsend/scripts/post-code.sh`
+
+```bash
+#!/usr/bin/env bash
+set -euo pipefail
+
+REPO_DIR="repo"
+
+if [ ! -d "${REPO_DIR}" ]; then
+  echo "error: extracted repo not found at ${REPO_DIR}" >&2
+  exit 1
+fi
+
+cd "${REPO_DIR}"
+
+BRANCH="$(git branch --show-current)"
+
+if [ -z "${BRANCH}" ] || [ "${BRANCH}" = "main" ]; then
+  echo "error: agent did not create a feature branch" >&2
+  exit 1
+fi
+
+git remote set-url origin \
+  "https://x-access-token:${GH_TOKEN}@github.com/${REPO_FULL_NAME}.git"
+
+git push -u origin "${BRANCH}"
+
+gh pr create \
+  --repo "${REPO_FULL_NAME}" \
+  --head "${BRANCH}" \
+  --title "fix: resolve #${ISSUE_NUMBER}" \
+  --body "Closes #${ISSUE_NUMBER}"
+```
+
+#### Behavior
+
+1. Verifies the extracted repo exists at `repo/` under `runDir` (the working
+   directory set by `run.go`).
+2. Verifies the agent created a feature branch (not `main`, not detached HEAD).
+3. Rewrites the git remote to use the GitHub App token for push auth.
+4. Pushes the branch.
+5. Creates a PR that references and auto-closes the originating issue.
+
+#### Error cases
+
+| Condition | Behavior |
+|---|---|
+| `repo/` missing | Exit 1 with message. Indicates extraction did not run. |
+| No branch or on `main` | Exit 1. Agent did not do its job. |
+| Push fails | `set -euo pipefail` exits immediately. |
+| PR creation fails | Same -- exits with `gh` error. |
+
+#### Environment contract
+
+| Variable | Source | Purpose |
+|---|---|---|
+| `GH_TOKEN` | Provider (github.yaml) | Push auth and `gh` CLI auth |
+| `REPO_FULL_NAME` | runner_env (code.yaml) | `owner/repo` for remote URL and PR target |
+| `ISSUE_NUMBER` | runner_env (code.yaml) | Issue reference in PR title/body |
+
+### Execution flow (in context of `run.go`)
+
+```
+fullsend run code
+  -> load harness/code.yaml
+  -> ensure provider "github" (GH_TOKEN available on host)
+  -> create sandbox, bootstrap agent, copy repo
+  -> run agent (agent commits to feature branch inside sandbox)
+  -> extract output files
+  -> [Marta] extract repo to runDir/repo/
+  -> delete sandbox
+  -> run post-script (scripts/post-code.sh) in runDir
+     -> push branch, create PR
+```
+
+The post-script runs in the deferred cleanup in `run.go`, after sandbox
+deletion but with access to the extracted repo and host environment.
+
+## What this does NOT cover
+
+- The `agents/code.md` agent definition
+- The `policies/code.yaml` sandbox network policy
+- Repo extraction from the sandbox (Marta's work)
+- Review agent integration (separate harness + post-script)
+- Retry/failure handling beyond immediate exit
+- PR labels, assignees, or reviewer assignment
+
+## Testing
+
+End-to-end testing requires repo extraction (in-flight). The post-script can be
+validated independently by:
+
+1. Creating a mock `runDir/repo/` with a git repo on a feature branch
+2. Setting `GH_TOKEN`, `REPO_FULL_NAME`, `ISSUE_NUMBER` in the environment
+3. Running `post-code.sh` and verifying push + PR creation against a test repo
+
+[adr-0017]: ../../ADRs/0017-credential-isolation-for-sandboxed-agents.md