Add agentic workflow to build latest F* master against latest Z3 master (#9733)

This introduces an agentic workflow that continuously validates Z3→F*
integration by building Z3 from this repository’s `master` and then
building `FStarLang/FStar` from its latest `master` using that exact Z3
binary.

- **Workflow added**
  - New source workflow: `.github/workflows/fstar-master-build.md`
- New compiled workflow: `.github/workflows/fstar-master-build.lock.yml`
  - Triggered on `daily` schedule and `workflow_dispatch`.

- **Build orchestration**
- Checks out Z3 `master` and builds/installs it with CMake + Ninja into
`/tmp/gh-aw/agent/z3-install`.
- Clones latest `FStarLang/FStar` `master` and records the exact commit
SHA used.
  - Forces F* build to use the locally built Z3 via:
    - `PATH=/tmp/gh-aw/agent/z3-install/bin:$PATH`
    - `Z3_EXE=/tmp/gh-aw/agent/z3-install/bin/z3`

- **Reporting + failure handling**
- On success: posts a discussion with Z3 commit/version, F* commit, and
command summary.
- On failure: opens an issue with failing phase, error summary, and log
excerpts.
- Uses safe-outputs with bounded lifetime (`expires: 14d`) and explicit
failure labeling.

```yaml
safe-outputs:
  create-discussion:
    title-prefix: "[F* Build] "
    close-older-discussions: true
    expires: 14d
  create-issue:
    title-prefix: "[F* Build Failure] "
    labels: ["build", "fstar"]
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

.github/workflows/fstar-master-build.md

@@ -0,0 +1,112 @@
+---
+description: Build latest FStar master using Z3 built from latest Z3 master
+
+on:
+  schedule: daily
+  workflow_dispatch:
+
+permissions: read-all
+
+network: defaults
+
+tools:
+  bash: true
+  github:
+    toolsets: [default]
+
+safe-outputs:
+  create-discussion:
+    title-prefix: "[F* Build] "
+    category: "Agentic Workflows"
+    close-older-discussions: true
+    expires: 14d
+  create-issue:
+    title-prefix: "[F* Build Failure] "
+    labels: ["build", "fstar"]
+  missing-tool:
+    create-issue: true
+  noop:
+    report-as-issue: false
+
+timeout-minutes: 120
+
+steps:
+  - name: Checkout Z3 master
+    uses: actions/checkout@v6.0.2
+    with:
+      ref: master
+      fetch-depth: 1
+      persist-credentials: false
+
+---
+
+# Build Latest F* with Latest Z3
+
+You are an automation engineer validating interoperability between Z3 and F*.
+
+Your goal is to build **latest Z3 master** from this repository, then build **latest FStarLang/FStar master** using the Z3 you built.
+
+## Requirements
+
+1. Use `${{ github.workspace }}` as the Z3 source (already checked out at `master`).
+2. Build Z3 from source with CMake + Ninja in Release mode.
+3. Install Z3 into `/tmp/gh-aw/agent/z3-install`.
+4. Verify the installed Z3 binary and capture its full version string.
+5. Fetch latest `master` from `FStarLang/FStar` and capture the exact commit SHA used.
+6. Build F* from that latest master using the locally built Z3 (not a system Z3).
+7. If F* requires setup steps, follow the current instructions from the checked-out FStar repository (for example `INSTALL.md`, `README.md`, `flake.nix`, or build scripts).
+8. Keep all temporary files under `/tmp/gh-aw/agent`.
+
+## Execution Plan
+
+### Phase 1: Environment Setup
+
+- Install required build dependencies for Z3 and F* (for example: `cmake`, `ninja-build`, `opam`, `m4`, `pkg-config`, `libgmp-dev`, `curl`, `git`, `python3`).
+- Print tool versions (`cmake`, `ninja`, `opam`, `ocaml` if available).
+
+### Phase 2: Build and Install Z3 (master)
+
+- Build in `/tmp/gh-aw/agent/z3-build`.
+- Use:
+  - `cmake -G Ninja -DCMAKE_BUILD_TYPE=Release`
+  - `ninja`
+  - `ninja install` with prefix `/tmp/gh-aw/agent/z3-install`
+- Verify:
+  - `/tmp/gh-aw/agent/z3-install/bin/z3 --version`
+- Record:
+  - Z3 commit from `git -C "${{ github.workspace }}" rev-parse HEAD`
+  - Z3 version output
+
+### Phase 3: Fetch Latest F* Master
+
+- Clone `https://github.com/FStarLang/FStar.git` into `/tmp/gh-aw/agent/fstar` with branch `master`.
+- Record exact commit SHA:
+  - `git -C /tmp/gh-aw/agent/fstar rev-parse HEAD`
+
+### Phase 4: Build F* with Local Z3
+
+- Ensure the local Z3 is used by exporting:
+  - `PATH=/tmp/gh-aw/agent/z3-install/bin:$PATH`
+  - `Z3_EXE=/tmp/gh-aw/agent/z3-install/bin/z3`
+- Discover and follow the repository’s current build path from checked-in docs/scripts.
+- Execute the build commands needed for F* master.
+- Capture concise logs into files under `/tmp/gh-aw/agent/logs/`.
+
+### Phase 5: Report Results
+
+- On success, call `create-discussion` with:
+  - Z3 commit + version
+  - FStar commit
+  - Key build commands executed
+  - Build outcome summary
+- On failure, call `create-issue` with:
+  - Failing phase
+  - Error summary
+  - Relevant log excerpt
+  - Z3 commit/version and FStar commit (if available)
+
+## Safety and Quality
+
+- Fail fast on command errors.
+- Do not modify repository files.
+- Keep the report concise and actionable.