# Design Document

## Overview
**Purpose**: This feature gives every XCE component (controller, scheduler, worker, apiserver, xcecli, xceadmin) a build-time identity — the git commit it was built from and when it was built — visible from the running artifact itself, via a `--version` flag and (for the four long-running daemons) a startup log line.

**Users**: Operators and developers diagnosing a running deployment (the motivating incident: a stale scheduler binary kept running a known-fixed crash, and confirming that required manual `ls -la` mtime checks plus `git merge-base --is-ancestor`).

**Impact**: Extends the existing, partial C-side mechanism (controller/scheduler already have a commit-id-only `--version` via `argp`, but `xce-build.sh` never actually sets it, so it is empty on every local build today) to carry a build timestamp too, fills the worker/Go/Python gaps, and fixes the `xce-build.sh` gap that made the motivating incident possible in the first place.

### Goals
- Every component's build artifact carries a git commit identifier (dirty-suffixed when applicable) and a build timestamp.
- `--version` on every component prints both and exits.
- Controller, scheduler, worker, and apiserver additionally log both at INFO level on startup.
- `xce-build.sh` (the dev-loop build path implicated in the motivating incident) actually sets these values — today it does not.
- The values are byte-for-byte identical between `--version` output and the startup log line for the same artifact.

### Non-Goals
- Automatically detecting or alerting that a *running* binary is stale relative to current source (out of scope per requirements' Boundary Context — this feature only makes the comparison possible).
- Version compatibility negotiation between components running different versions.
- Retrofitting version info into already-built/deployed binaries.
- Migrating worker's `getopt_long()` argument parsing to `argp` (a much larger, unrelated change) — worker gets a hand-added `--version` case instead.

## Boundary Commitments

### This Spec Owns
- The two build-time values themselves (commit identifier, build timestamp) and how each of the six components' build steps receive them.
- `--version` output and (for the four daemons) the startup log line, for all six components.
- `xce-build.sh`'s computation of both values for the dev-loop build path.
- The nix packages' (`xce.nix`, `xcecli.nix`) computation of both values for the production build path.

### Out of Boundary
- Any runtime mechanism that compares a running binary's version against "current" source (no such comparison exists or is planned).
- `xceadmin`'s own semantic package version (`pyproject.toml`'s `version = "0.1.0"`) — untouched; build metadata is additive, displayed alongside it, not a replacement for it.
- Worker's broader argument-parsing architecture.

### Allowed Dependencies
- The existing `commit_id` meson option and `VERSION_COMMIT_ID`/`MK_VERSION` C mechanism (`src/meson.build`, `src/meson.options`, `src/include/utils.h`) — extended, not replaced.
- The existing Nix flake commit-id derivation (`self.shortRev`/`self.dirtyShortRev`, `src/flake.nix`) — extended with a new build-time value, same wiring style.
- `src/tools/go_build`'s existing env-var-driven `go build` invocation pattern (already used for CGO flags).
- `src/xceadmin/meson.build`'s existing `custom_target` → `meson-build.sh` argument-passing pattern.
- Go's standard `-ldflags -X` package-variable injection; Cobra's built-in `Version` field (xcecli already uses Cobra); Click's built-in `version_option` (xceadmin already uses Click).

### Revalidation Triggers
- The `commit_id` meson option is renamed, removed, or its consumption in `src/include/utils.h`'s `MK_VERSION`/`STR` macros changes shape.
- `xce-build.sh`'s `MESON_OPTS` construction is refactored away from its current per-profile array pattern.
- `src/tools/go_build`'s final `go build` invocation line changes.
- `src/xceadmin/meson-build.sh`'s step ordering changes (the generated build-info module must land before the `pip install` step that packages it).

## Architecture

### Existing Architecture Analysis
- Controller and scheduler already parse `--version`/`-V` for free via GNU `argp`'s `argp_program_version` mechanism (`MK_VERSION("xce v0.0.1-", STR(VERSION_COMMIT_ID))`, both `main.c`s) — this feature extends that same macro rather than adding a parallel one.
- `VERSION_COMMIT_ID` already flows into every C component uniformly via `add_project_arguments()` at the top-level `src/meson.build` — the new build-timestamp define follows the identical path, added once, inherited everywhere.
- Worker's `getopt_long()`-based parsing has no equivalent auto-version behavior and needs an explicit new case.
- `git` is deliberately absent from the nix devShell's declared buildInputs (`src/nixSupport/xce.nix`) — the *sandboxed* `nix build` path already avoids shelling out to git for exactly this reason (uses Nix's own `self.shortRev` introspection instead). The *dev-loop* `xce-build.sh` path runs inside `nix develop`, which layers onto the ambient host PATH rather than replacing it, so git IS usable there — and needs to be used there, since `xce-build.sh` today never sets `commit_id` at all (the actual gap behind the motivating incident).

### Architecture Pattern & Boundary Map
Two independent **computation sites** (respecting the existing sandboxed-vs-ambient split) feed one **resolved value pair** into meson, which every language-specific **consumption site** reads from — never recomputes independently.

```mermaid
graph TB
    DevScript[xce-build.sh git plus date]
    NixPkg[xce.nix xcecli.nix self.shortRev plus preConfigure date]
    MesonOpts[meson commit_id and build_time options]
    CDefine[C VERSION_COMMIT_ID and VERSION_BUILD_TIME defines]
    GoLdflags[go_build ldflags -X injection]
    PyGen[meson-build.sh generated build info module]
    Controller[controller and scheduler argp version]
    Worker[worker getopt_long version case]
    Apiserver[apiserver flag version]
    Xcecli[xcecli cobra version]
    Xceadmin[xceadmin click version_option]

    DevScript --> MesonOpts
    NixPkg --> MesonOpts
    MesonOpts --> CDefine
    MesonOpts --> GoLdflags
    MesonOpts --> PyGen
    CDefine --> Controller
    CDefine --> Worker
    GoLdflags --> Apiserver
    GoLdflags --> Xcecli
    PyGen --> Xceadmin
```

**Architecture Integration**:
- Selected pattern: single resolved-value-pair fan-out, matching the existing `commit_id` mechanism's own shape.
- Domain/feature boundaries: computation (2 sites, environment-specific) is fully separated from consumption (6 sites, one per component) — a consumption site never knows or cares which computation site produced its value.
- Existing patterns preserved: `argp` version macro (C), Cobra `Version` field and Click `version_option` (already the idiomatic mechanism in each respective Go/Python tool), `go_build`'s env-var plumbing, `meson-build.sh`'s positional-arg plumbing.
- New components rationale: `sim_prescan_session_count`-style small, single-purpose additions only where a gap genuinely exists (worker's version case, Go's ldflags wiring, Python's generated module) — no new abstraction layer introduced.
- Steering compliance: no new external dependency (`tech.md`); wire/build-format changes are free pre-release (no back-compat burden); TDD required for every new behavior.

### Technology Stack

| Layer | Choice / Version | Role in Feature | Notes |
|-------|------------------|-----------------|-------|
| C build (controller/scheduler/worker) | Meson preprocessor defines (existing mechanism) | Carries `commit_id` (existing) + new `build_time` into every C translation unit | `src/meson.build:30` |
| C CLI (controller/scheduler) | GNU `argp` (existing) | `--version`/`-V` auto-handling via `argp_program_version` | Extend `MK_VERSION` macro |
| C CLI (worker) | `getopt_long()` (existing) | New explicit `--version` case | No parser migration |
| Go build | `-ldflags -X` (standard Go idiom, new to this repo) | Injects `main.GitCommit`/`main.BuildTime` package vars | Via `go_build` script + `Makefile` |
| Go CLI (apiserver) | `flag` package (existing) | New `-version` flag | Matches existing single-flag style |
| Go CLI (xcecli) | Cobra (existing) | `rootCmd.Version` field (built-in `--version`) | Zero new parsing code |
| Python build | Meson `custom_target` (existing) | New generated build-info module written before `pip install` | `meson-build.sh` |
| Python CLI (xceadmin) | Click (existing) | `click.version_option()` (built-in `--version`) | Zero new parsing code |
| Nix packaging | Nix flake (existing) | `self.shortRev`/`self.dirtyShortRev` (existing, eval-time) + a `preConfigure` build-phase `date -u` hook for build_time (task 2.2 round 2: `builtins.currentTime` was tried first but breaks pure-eval `nix build`, i.e. requires `--impure`, and yields non-UTC epoch seconds — rejected in review, corrected to a build-phase computation) | `xce.nix`, `xcecli.nix` |

## File Structure Plan

### Modified Files
- `src/meson.options` — add a `build_time` string option (default `''`), alongside the existing `commit_id`.
- `src/meson.build` — add `-DVERSION_BUILD_TIME=` to the existing `add_project_arguments()` call (line ~30).
- `src/include/utils.h` — extend `MK_VERSION`/introduce a companion macro so the version string includes the build time, not just the commit id.
- `src/controller/main.c`, `src/scheduler/src/main.c` — update `argp_program_version` construction to include build time; add the startup INFO log line (each already has one startup INFO call site to extend/follow).
- `src/worker/src/main.c` — add a `--version` long option + case (prints the same shape, exits 0); add the startup INFO log line (follows its own existing startup INFO call site).
- `src/tools/xce-build.sh` — compute `commit_id` (git, `-dirty` suffixed) and `build_time` (UTC `date`) and pass both via new `-Dcommit_id=`/`-Dbuild_time=` entries in `MESON_OPTS`, falling back to `"unknown"` if `git` fails (e.g. not a git checkout).
- `src/nixSupport/xce.nix`, `src/nixSupport/xcecli.nix` — a `preConfigure` build-phase hook runs `date -u +%Y-%m-%dT%H:%M:%SZ` and appends `-Dbuild_time=` to `mesonFlagsArray` (build-time, not eval-time, unlike `commit_id`'s `self.shortRev` wiring in `src/flake.nix`/`src/nixSupport/default.nix`, which is unchanged).
- `src/tools/go_build` — read `XCE_GIT_COMMIT`/`XCE_BUILD_TIME` env vars (empty-safe) and append `-ldflags "-X main.GitCommit=... -X main.BuildTime=..."` to the final `go build` invocation.
- `src/frontend/apiserver/meson.build`, `src/frontend/xcecli/meson.build` — pass the two new env vars into their `custom_target()` calls (mirrors existing env var passing).
- `src/frontend/Makefile` — add the same `-ldflags` construction (via `git`/`date` directly, dev-loop path) to `build-server`/`build-cli` targets.
- `src/frontend/apiserver/cmd/main.go` — declare `var (GitCommit, BuildTime string)`; add a `-version` flag; add/extend the startup `logger.Info(...)` line.
- `src/frontend/xcecli/cmd/main.go` — declare the same two vars; set `rootCmd.Version` (Cobra); extend its own startup `logger.Info(...)` line.
- `src/xceadmin/meson.build` — pass two new positional args (or env vars) to `meson-build.sh`.
- `src/xceadmin/meson-build.sh` — write a small generated Python module (e.g. `_build_info.py`) into the mirrored source tree, before the `pip install` step, containing the two values (falls back to `"unknown"` if not provided).
- `src/xceadmin/src/xceadmin/cli.py` — read the generated module (import guarded for the case it's genuinely absent, e.g. a non-meson editable install) and wire `click.version_option()` on the top-level group.

### New Files
- `src/xceadmin/src/xceadmin/_build_info.py` — **generated at build time only** (not checked in); a committed fallback stub (all fields `"unknown"`) ships in-tree so `pip install -e .` (the documented fast-iteration path in `build-deployment.md`) still imports cleanly without having run the meson build.

> No new C/Go/Python source files beyond the one generated-with-fallback-stub Python module above — every other change extends an existing file's existing responsibility (arg parsing gains a flag, a build script gains an option).

## Requirements Traceability

| Requirement | Summary | Components | Interfaces | Flows |
|-------------|---------|------------|------------|-------|
| 1.1, 1.2 | Every artifact carries commit id + build time | All 6 consumption sites + both computation sites | `MK_VERSION` macro, Go ldflags vars, Python `_build_info` module | Computation → meson → consumption |
| 1.3 | Dirty tree marked | `xce-build.sh`'s git computation | commit_id string carries `-dirty` suffix | n/a |
| 1.4 | Unknown when undeterminable | `xce-build.sh`, `meson-build.sh`, `go_build` | fallback to literal `"unknown"` | n/a |
| 2.1 | `--version` prints and exits | argp (controller/scheduler), worker's new case, apiserver's `-version`, Cobra `Version`, Click `version_option` | six CLI entry points | n/a |
| 2.2 | `--version` and startup log agree | shared macro/var/module per component | same source value read twice, never recomputed | n/a |
| 3.1, 3.2 | Startup log line at INFO | controller/scheduler/worker/apiserver startup sequences | existing first-INFO-line call sites, extended | Startup → log |
| 4.1, 4.2 | Build tooling confirms embedding | `xce-build.sh`, nix packages | non-empty resolved value check before/after `meson setup`/build | Build → verify |
| 4.3 | Accurate under every C build profile | `src/meson.build`'s project-wide `add_project_arguments()` | applies uniformly to asan/debug/release | n/a |
| 5.1, 5.2 | Values reflect actual tree/build event | `xce-build.sh` (git+date at invocation time), nix (`self.shortRev` at evaluation time + `preConfigure` `date -u` at build time) | no hardcoded/stale values | n/a |

## Components and Interfaces

### C Daemons (controller, scheduler, worker)

#### Version macro
| Field | Detail |
|-------|--------|
| Intent | Carry commit id + build time into every C daemon's `--version` output and startup log |
| Requirements | 1.1, 1.2, 2.1, 2.2, 3.1, 3.2, 4.3 |

**Responsibilities & Constraints**
- `MK_VERSION` (`src/include/utils.h`) extended to compose `"xce v0.0.1-<commit_id> built <build_time>"` (or equivalent) from the two new preprocessor defines — a single macro, both consumers (controller/scheduler's `argp_program_version`, worker's hand-added case) call it, guaranteeing `--version` and the startup log line render from the identical string.
- Controller/scheduler: their existing single startup INFO line (`main.c:365`/`377`+`381` respectively, per discovery) gets this version string appended or logged as an immediately-preceding line — never a second, independently-formatted string.
- Worker: new `{"version", no_argument, NULL, OPT_VERSION}` long option in its existing `long_opts[]`/`getopt_long()` switch (`main.c:358-364`), printing the same macro's output and exiting 0 before any other startup work begins.

**Contracts**: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [ ]

**Implementation Notes**
- Integration: extends `src/include/utils.h`'s existing `STR`/`MK_VERSION` macros — no new header.
- Validation: a build with `commit_id`/`build_time` unset must still compile and print `"unknown"` fields, never a blank/garbled string.
- Risks: worker's `getopt_long()` short-option string (`"n:l:vh"`) must gain a way to reach the new long-only option — use a long-option-only constant (no short equivalent), matching `--peers`'s own existing precedent in the same `long_opts[]` array.

### Go Binaries (apiserver, xcecli)

#### ldflags version injection
| Field | Detail |
|-------|--------|
| Intent | Inject build-time values into each Go binary at link time, exposed via each CLI's native version mechanism |
| Requirements | 1.1, 1.2, 2.1, 2.2, 3.1, 3.2, 4.1, 4.2 |

**Responsibilities & Constraints**
- `src/tools/go_build` (consumed by both `apiserver/meson.build` and `xcecli/meson.build`'s `custom_target()`) reads `XCE_GIT_COMMIT`/`XCE_BUILD_TIME` from its environment (empty-safe — falls back to `"unknown"` when unset, e.g. a bare `go build` invoked by hand) and appends `-ldflags "-X main.GitCommit=$v1 -X main.BuildTime=$v2"` to its existing `go build` invocation.
- `src/frontend/Makefile`'s `build-server`/`build-cli` targets compute the same two values directly (git/date, dev-loop path, no meson involved) and pass the identical `-ldflags` shape — same output format as the meson path, different computation site (mirrors the C-side split).
- `apiserver/cmd/main.go`: package-level `var (GitCommit = "unknown"; BuildTime = "unknown")`, a new `-version` bool flag (checked first, before `utils.InitLogger()` — prints and exits, no logging side effects), and the existing `logger.Info("********** Initialize Logger done!")` call site extended to also log both values (same convention, `"********** <action> done!"` is untouched; the version fields ride as structured zap fields on that same line or an adjacent one).
- `xcecli/cmd/main.go`: same two vars; version string passed into `router.Execute(cm, version)`, which sets `rootCmd.Version` before `rootCmd.Execute()` runs (Cobra then handles `--version` natively — zero new flag-parsing code). Correction (task 4.5): xcecli's startup log is deliberately NOT extended — Requirement 3 scopes the startup-log obligation to "the controller, scheduler, worker, or apiserver daemon" only; xcecli is a one-shot CLI, not a daemon, and was never in Requirement 3's scope.

**Contracts**: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [ ]

**Implementation Notes**
- Integration: `go_build`'s env-var pattern already exists for CGO flags — this reuses it, not a new plumbing mechanism.
- Validation: `--version`/`-version` output and the startup log's values must be the exact same two package vars, read twice, never two separate computations.
- Risks: none identified — `-ldflags -X` only accepts string vars, both fields are strings by construction.

### Python (xceadmin)

#### Generated build-info module
| Field | Detail |
|-------|--------|
| Intent | Package build-time values into the wheel so `xceadmin --version` reflects the actual build, not just `pyproject.toml`'s static semantic version |
| Requirements | 1.1, 1.2, 2.1, 4.1, 4.2 |

**Responsibilities & Constraints**
- `meson-build.sh` writes `_build_info.py` (containing `GIT_COMMIT`/`BUILD_TIME` string constants, sourced from two new args/env vars, `"unknown"` fallback) into the mirrored source tree's `xceadmin/` package directory, *before* the `pip install` step (so it packages into both the dev venv install and the final wheel) — same ordering discipline the existing schema-sync step already follows (also runs before `pip install`).
- `cli.py`'s top-level `@click.group()` gains `@click.version_option(version=f"{pkg_version} ({_build_info.GIT_COMMIT}, {_build_info.BUILD_TIME})")`, importing `_build_info` defensively (a committed fallback stub with `"unknown"` fields ships in-tree so a non-meson `pip install -e .` — the documented fast-iteration path — still imports cleanly).
- No startup log line (Requirement 3 scopes that to the four long-running daemons only; xceadmin is a one-shot CLI).

**Contracts**: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [ ]

**Implementation Notes**
- Integration: extends `meson-build.sh`'s existing custom_target sequence at exactly one new step, same file-write style already used for schema sync.
- Validation: `pip install -e .` (no meson) must still import cleanly against the committed fallback stub — this is the one file in this feature that must exist in two states (checked-in fallback vs. build-time-overwritten real values) and both must be valid Python.
- Risks: the generated module must not be checked in with real values (would go stale immediately) — only the `"unknown"`-only fallback stub is committed; `.gitignore` (or equivalent) must exclude the real generated file if `meson-build.sh` ever writes it into the actual source tree rather than only the mirrored build-tree copy (verify this during implementation — the mirroring step at `meson-build.sh` lines 32-46 should already keep it out of the real source tree, matching how the schema sync step works today).

### Build Orchestration

#### xce-build.sh value computation
| Field | Detail |
|-------|--------|
| Intent | Close the actual gap behind the motivating incident — the dev-loop build path must set real values, not leave them empty |
| Requirements | 4.1, 4.2, 4.3, 5.1, 5.2 |

**Responsibilities & Constraints**
- Computes `commit_id` via `git rev-parse --short HEAD`, appending `-dirty` when `git diff --quiet HEAD --` (or `git status --porcelain`) reports changes; falls back to `"unknown"` if `git` itself fails (e.g. run against an extracted source tarball with no `.git`).
- Computes `build_time` via `date -u +%Y-%m-%dT%H:%M:%SZ`.
- Appends `-Dcommit_id="$commit_id" -Dbuild_time="$build_time"` to `MESON_OPTS` (`xce-build.sh:70-72`) for every profile, before the existing `meson setup`/`meson setup --reconfigure` calls.

**Contracts**: Service [ ] / API [ ] / Event [ ] / Batch [ ] / State [ ]

**Implementation Notes**
- Integration: a small addition right where `MESON_OPTS` is already constructed — no restructuring of the profile dispatch.
- Validation: the exact scenario from the motivating incident — build via `/xce-build scheduler debug`, run `--version`, confirm it shows a real (non-empty, non-"unknown") commit id matching `git rev-parse --short HEAD` at build time.
- Risks: none — purely additive to an existing array.

## Testing Strategy

### Unit Tests
- C: a new scheduler/controller/worker test (or a shared `lib` test if `MK_VERSION`'s logic is factored into a testable helper) asserting the version string contains both the commit id and build time defines when set, and `"unknown"` fallbacks when unset.
- Go: a test in each `cmd` package (or a shared helper) asserting `-version`/`--version` output contains both `GitCommit` and `BuildTime` values.
- Python: a `pytest` case (xceadmin's existing suite, run by `meson-build.sh`) asserting `xceadmin --version` output contains the generated build-info fields, and that the committed fallback stub is itself valid, importable Python.

### Integration Tests
- `xce-build.sh`-driven build (any profile) followed by running `--version` on the resulting controller/scheduler/worker binaries, asserting a real (non-`"unknown"`) commit id is present — this is the regression test for the motivating incident itself.
- A `go_build`-driven meson build of apiserver/xcecli, followed by `-version`, asserting the same.
- `xceadmin`'s existing meson-driven build+test+wheel cycle, followed by installing the wheel and running `xceadmin --version`.

### E2E / Consistency
- For at least one C daemon and one Go binary: start it, capture its startup log line, separately run `--version`, and assert the two report byte-identical commit id and build time (Requirement 2.2).