fix: support Gitea 28.0.0 mail templates

COMPATIBILITY.md

@@ -7,12 +7,13 @@ This document tracks the compatibility between **Gitea Mail Templates** releases
 <!-- TRACKER:QUICK-REF-MAX OFFSET=3 -->
 | Template Release | Min Gitea | Max Tested Gitea | Status |
 |-----------------|-----------|-----------------|--------|
-| **v1.27.3** | **1.25.0** | **1.27.3** | ✅ Active |
+| **v28.0.0** | **28.0.0** | **28.0.0** | ✅ Active |
+| **v1.27.3** | **1.25.0** | **1.27.3** | ✅ Superseded; release emails fail on Gitea 28.0.0 (`FileSize` removed) |
 | **v1.27.2** | **1.25.0** | **1.27.3** | ⚠️ Push notices fail in Bloom, Ember, and Heritage on Gitea 1.27.1+ |
 | **v1.0.1**      | **1.25.0** | **1.27.0** | ✅ Superseded; push notices need newer release on 1.27.1+ |
 | **v1.0.0**      | **1.25.0** | **1.26.4** | ✅ Superseded |
 
-> **Latest verified:** Release v1.27.3 passes the Gitea 1.27.3 source audit and push-render test. The older v1.27.2 archive contains three broken push-notification templates. <!-- TRACKER:LATEST-VERIFIED -->
+> **Latest verified:** Release v28.0.0 passes the Gitea 28.0.0 mail-template, mailer-context, function, and translation-key source audit plus all-theme rendering tests. This release requires Gitea 28.0.0; use v1.27.3 for Gitea 1.25.0–1.27.3. <!-- TRACKER:LATEST-VERIFIED -->
 
 ## Versioning
 
@@ -20,6 +21,7 @@ The release tag identifies the downloadable template package. The supported Gite
 
 | Gitea version | Template release |
 |---------------|------------------|
+| 28.0.0        | **v28.0.0**; older releases use the removed `FileSize` function in release emails |
 | 1.27.3        | **v1.27.3**; v1.27.2 has a push-notification issue in three themes |
 | 1.27.2        | **v1.27.3**; v1.27.2 has the same issue |
 | 1.27.1        | **v1.27.3**; v1.27.2 has the same issue |
@@ -27,6 +29,7 @@ The release tag identifies the downloadable template package. The supported Gite
 - The [tracker workflow](.github/workflows/gitea-tracker.yml) opens a PR when a new Gitea release appears, marking it ⏳ Pending Verification.
 - After verification, update the top **Template Release** row. Keep fixes on `main` marked **unreleased** until a new tag is published; the [release workflow](.github/workflows/release.yml) packages the archive on tag push.
 - The older `v1.0.1` tag predates the Gitea 1.27.1 push notification data fix and should not be used for Gitea 1.27.1 or newer.
+- Gitea 28.0.0 replaces the mail-template `FileSize` function with `FormatByteSize`. The two functions are not interchangeable across these Gitea versions; use the matching template release.
 
 ## Check Your Gitea Version
 
@@ -41,6 +44,7 @@ gitea --version
 <!-- TRACKER:VERSION-INSERT OFFSET=2 -->
 | Gitea | Release Date | Mail Template Changes | Breaking? |
 |-------|-------------|----------------------|-----------|
+| **28.0.0** | 2026-09-29 | `FileSize` removed and `FormatByteSize` added; mail templates now have `mail/`-prefixed internal names and shared head/footer partials; workflow emails gain status-icon fields. Our custom template paths and referenced data fields remain valid. | **Yes** (release attachment formatting) |
 | **1.27.3** | 2026-08-29 | No upstream mail template, mailer, or locale changes; an existing push-notification defect in three themes is fixed in template release v1.27.3 | No upstream break |
 | **1.27.2** | 2026-08-14 | None — security + bug fixes | No |
 | **1.27.1** | 2026-07-27 | Push commit data paths changed: .ID → .UserCommit.GitCommit.ID (#38467); older custom templates can fail on push notifications | Yes (old .ID paths) |
@@ -69,7 +73,7 @@ All 11 template types use only Gitea built-in variables and functions. Verified
 | `QueryEscape` | ≤ 1.21 | URL query encoding |
 | `PathEscapeSegments` | ≤ 1.21 | Per-segment path encoding |
 | `ShortSha` | ≤ 1.21 | Truncated commit hash |
-| `FileSize` | ≤ 1.21 | Human-readable file size |
+| `FormatByteSize` | 28.0.0 | Human-readable IEC file size; replaces `FileSize` |
 | `HTMLFormat` | ≤ 1.21 | Render string as safe HTML |
 | `Iif` | ≤ 1.21 | Inline conditional |
 | `dict` | ≤ 1.21 | Build maps from key-value pairs |
@@ -100,13 +104,14 @@ All 11 template types use only Gitea built-in variables and functions. Verified
 
 ### Translation Keys
 
-All templates use Gitea's official `mail.*` translation namespace. Keys are stable across Gitea 1.25+.
+All templates use Gitea's official `mail.*` translation namespace. Every referenced key was checked against Gitea 28.0.0's English locale file.
 
 ## How Compatibility Is Verified
 
-1. **Automated lint** — CI renders all templates via `go run . preview all` on every push
+1. **Automated lint** — CI renders all templates via `go run . preview all` on every push; the preview function map mirrors Gitea 28.0.0
 2. **Source audit** — Template data contexts are cross-referenced against Gitea's `services/mailer/` package
-3. **Release checklist** — Each release confirms the max-tested Gitea version in this file
+3. **Regression tests** — Go tests render push notifications and release attachments in all 10 themes
+4. **Release checklist** — Each release confirms the max-tested Gitea version in this file
 
 ## Automated Tracking