Add the Tazel plugin catalog of ViGet to the API

ViGet opens in stages: first only Progmasoft publishes Tazel plugins, later
every account. This adds the catalog and the server-side publishing for the
first stage; nothing publishes through the API yet.

- ViGet/: the catalog of Tazel plugins (in memory, or in PostgreSQL beside
  the accounts with its own numbered schema steps), the descriptor read from
  the JAR (META-INF/tazel-plugin.properties, with a reader of the Java
  properties format, and the ProjectPlugin service entry), and publishing:
  the publisher must be in ViGet:TazelPublishers (Progmasoft for now) and an
  existing account of that exact name, a version is never replaced, names
  that differ only in letter case are refused, and ViGet needs a
  description, an author and a license. The JAR is kept at
  dslplugins/tazel/<Publisher>/<Name>/<Version>/<Name>-<Version>.jar below
  ViGet:ArtifactRoot.
- Read endpoints under /api/v1/viget/dslplugins/tazel: the list, a plugin,
  and index.json, the index Tazel reads.
- 'viget publish-tazel-plugin <jar>' and 'viget yank-tazel-plugin' run with
  the configuration of the service instead of the service.
- The account store can find an account by name.

The pages, the Nginx routes and the deployment follow.

8 files changed, 1166 insertions, 0 deletions

diff --git a/apps/api/ViGet/JavaProperties.cs b/apps/api/ViGet/JavaProperties.cs
new file mode 100644
index 0000000..e55991e
--- /dev/null
+++ b/apps/api/ViGet/JavaProperties.cs
@@ -0,0 +1,149 @@
+// SPDX-FileCopyrightText: 2026 Progmasoft <support@progmasoft.com>
+// SPDX-License-Identifier: AGPL-3.0-or-later WITH AdditionRef-Progmasoft-Patent-Grant-1.1
+
+using System.Globalization;
+using System.Text;
+
+namespace Progmasoft.Progmaweb.Api.ViGet;
+
+/// <summary>Reads the text of a Java <c>.properties</c> file, as <c>java.util.Properties.load</c> does.</summary>
+/// <remarks>
+/// A logical line may continue over several lines with a trailing backslash; <c>#</c> and <c>!</c> start a comment
+/// line; a key ends at the first unescaped <c>=</c>, <c>:</c> or white space; and <c>\t</c>, <c>\n</c>, <c>\r</c>,
+/// <c>\f</c> and <c>\uXXXX</c> are escapes, while a backslash before any other character stands for that character.
+/// A later line with the same key replaces an earlier one.
+/// </remarks>
+internal static class JavaProperties
+{
+    /// <summary>Reads the properties of a text.</summary>
+    /// <param name="text">The text of the file, already decoded.</param>
+    /// <returns>The properties by key.</returns>
+    /// <exception cref="FormatException">A <c>\u</c> escape is not followed by four hexadecimal digits.</exception>
+    public static IReadOnlyDictionary<string, string> Parse(string text)
+    {
+        Dictionary<string, string> properties = new(StringComparer.Ordinal);
+        foreach (string line in LogicalLines(text))
+        {
+            int index = 0;
+            while (index < line.Length && IsBlank(line[index]))
+            {
+                index++;
+            }
+
+            if (index == line.Length || line[index] is '#' or '!')
+            {
+                continue;
+            }
+
+            int keyStart = index;
+            while (index < line.Length && !IsKeyEnd(line[index]))
+            {
+                index += line[index] == '\\' ? 2 : 1;
+            }
+
+            string key = Unescape(line[keyStart..Math.Min(index, line.Length)]);
+            while (index < line.Length && IsBlank(line[index]))
+            {
+                index++;
+            }
+
+            if (index < line.Length && line[index] is '=' or ':')
+            {
+                index++;
+                while (index < line.Length && IsBlank(line[index]))
+                {
+                    index++;
+                }
+            }
+
+            properties[key] = Unescape(line[index..]);
+        }
+
+        return properties;
+    }
+
+    /// <summary>Joins the physical lines that a trailing backslash continues.</summary>
+    private static IEnumerable<string> LogicalLines(string text)
+    {
+        string[] lines = text.Replace("\r\n", "\n", StringComparison.Ordinal).Replace('\r', '\n').Split('\n');
+        StringBuilder current = new();
+        bool continuing = false;
+        foreach (string physical in lines)
+        {
+            // A continued line loses the white space it starts with.
+            string line = continuing ? physical.TrimStart(' ', '\t', '\f') : physical;
+            int backslashes = 0;
+            for (int position = line.Length - 1; position >= 0 && line[position] == '\\'; position--)
+            {
+                backslashes++;
+            }
+
+            continuing = backslashes % 2 == 1;
+            current.Append(continuing ? line[..^1] : line);
+            if (!continuing)
+            {
+                yield return current.ToString();
+                current.Clear();
+            }
+        }
+
+        if (current.Length > 0)
+        {
+            yield return current.ToString();
+        }
+    }
+
+    private static bool IsBlank(char character) => character is ' ' or '\t' or '\f';
+
+    private static bool IsKeyEnd(char character) => character is '=' or ':' || IsBlank(character);
+
+    private static string Unescape(string text)
+    {
+        StringBuilder result = new(text.Length);
+        for (int index = 0; index < text.Length; index++)
+        {
+            char character = text[index];
+            if (character != '\\' || index + 1 == text.Length)
+            {
+                result.Append(character);
+                continue;
+            }
+
+            char escaped = text[++index];
+            switch (escaped)
+            {
+                case 't':
+                    result.Append('\t');
+                    break;
+                case 'n':
+                    result.Append('\n');
+                    break;
+                case 'r':
+                    result.Append('\r');
+                    break;
+                case 'f':
+                    result.Append('\f');
+                    break;
+                case 'u':
+                    if (text.Length - index - 1 < 4 ||
+                        !int.TryParse(
+                            text.AsSpan(index + 1, 4),
+                            NumberStyles.AllowHexSpecifier,
+                            CultureInfo.InvariantCulture,
+                            out int code))
+                    {
+                        throw new FormatException("A \\u escape needs four hexadecimal digits.");
+                    }
+
+                    result.Append((char)code);
+                    index += 4;
+                    break;
+                default:
+                    result.Append(escaped);
+                    break;
+            }
+        }
+
+        return result.ToString();
+    }
+}
diff --git a/apps/api/ViGet/PostgresTazelPluginCatalog.cs b/apps/api/ViGet/PostgresTazelPluginCatalog.cs
new file mode 100644
index 0000000..07fa86f
--- /dev/null
+++ b/apps/api/ViGet/PostgresTazelPluginCatalog.cs
@@ -0,0 +1,309 @@
+// SPDX-FileCopyrightText: 2026 Progmasoft <support@progmasoft.com>
+// SPDX-License-Identifier: AGPL-3.0-or-later WITH AdditionRef-Progmasoft-Patent-Grant-1.1
+
+using Npgsql;
+
+namespace Progmasoft.Progmaweb.Api.ViGet;
+
+/// <summary>The tables of <see cref="PostgresTazelPluginCatalog"/> and the steps that bring a database to them.</summary>
+/// <remarks>
+/// The same numbered steps as the account tables, in a version table of their own, <c>viget_schema_versions</c>.
+/// A step is never edited after it has been released.
+/// </remarks>
+internal static class ViGetSchema
+{
+    /// <summary>Key of the advisory lock that lets one process at a time change these tables.</summary>
+    private const long MigrationLockKey = 0x5669476574;
+
+    private static readonly string[] Steps =
+    [
+        // 1: Tazel plugins and their versions.
+        //
+        // A plugin is named by its publisher and its name as they are spelled; the unique index on their upper
+        // case keeps two plugins from differing only in letter case. A version is never removed, only yanked.
+        """
+        CREATE TABLE viget_tazel_plugins (
+            publisher   text        NOT NULL,
+            name        text        NOT NULL,
+            description text,
+            authors     text[]      NOT NULL,
+            license     text,
+            homepage    text,
+            repository  text,
+            updated_at  timestamptz NOT NULL,
+            PRIMARY KEY (publisher, name)
+        );
+
+        CREATE UNIQUE INDEX viget_tazel_plugins_folded_key ON viget_tazel_plugins (upper(publisher), upper(name));
+
+        CREATE TABLE viget_tazel_plugin_versions (
+            publisher    text        NOT NULL,
+            name         text        NOT NULL,
+            version      text        NOT NULL,
+            sha256       text        NOT NULL,
+            api_version  integer     NOT NULL,
+            size         bigint      NOT NULL,
+            published_at timestamptz NOT NULL,
+            yanked       boolean     NOT NULL DEFAULT false,
+            PRIMARY KEY (publisher, name, version),
+            FOREIGN KEY (publisher, name) REFERENCES viget_tazel_plugins (publisher, name)
+        );
+        """
+    ];
+
+    /// <summary>The version a database has after every step.</summary>
+    public static int CurrentVersion => Steps.Length;
+
+    /// <summary>Takes the steps a database has not taken yet, in one transaction.</summary>
+    /// <returns>The number of steps that were taken.</returns>
+    /// <exception cref="InvalidOperationException">The database has taken steps this program does not know.</exception>
+    public static async Task<int> ApplyAsync(NpgsqlDataSource dataSource, CancellationToken cancellationToken)
+    {
+        await using NpgsqlConnection connection = await dataSource.OpenConnectionAsync(cancellationToken);
+        await using NpgsqlTransaction transaction = await connection.BeginTransactionAsync(cancellationToken);
+        await ExecuteAsync(connection, transaction, $"SELECT pg_advisory_xact_lock({MigrationLockKey})", cancellationToken);
+        await ExecuteAsync(
+            connection,
+            transaction,
+            """
+            CREATE TABLE IF NOT EXISTS viget_schema_versions (
+                version    integer     PRIMARY KEY,
+                applied_at timestamptz NOT NULL DEFAULT now()
+            )
+            """,
+            cancellationToken);
+
+        int version;
+        await using (NpgsqlCommand read = new(
+            "SELECT coalesce(max(version), 0) FROM viget_schema_versions", connection, transaction))
+        {
+            version = (int)(await read.ExecuteScalarAsync(cancellationToken))!;
+        }
+
+        if (version > Steps.Length)
+        {
+            throw new InvalidOperationException(
+                $"The ViGet tables are at schema version {version}, and this program knows version {Steps.Length}.");
+        }
+
+        int taken = 0;
+        for (int step = version; step < Steps.Length; step++)
+        {
+            await ExecuteAsync(connection, transaction, Steps[step], cancellationToken);
+            await using NpgsqlCommand record = new(
+                "INSERT INTO viget_schema_versions (version) VALUES ($1)", connection, transaction);
+            record.Parameters.AddWithValue(step + 1);
+            await record.ExecuteNonQueryAsync(cancellationToken);
+            taken++;
+        }
+
+        await transaction.CommitAsync(cancellationToken);
+        return taken;
+    }
+
+    private static async Task ExecuteAsync(
+        NpgsqlConnection connection,
+        NpgsqlTransaction transaction,
+        string sql,
+        CancellationToken cancellationToken)
+    {
+        await using NpgsqlCommand command = new(sql, connection, transaction);
+        await command.ExecuteNonQueryAsync(cancellationToken);
+    }
+}
+
+/// <summary>The Tazel plugins of ViGet in PostgreSQL, beside the accounts.</summary>
+/// <param name="dataSource">Connections to the database of the accounts.</param>
+internal sealed class PostgresTazelPluginCatalog(NpgsqlDataSource dataSource) : ITazelPluginCatalog
+{
+    private const string PluginColumns = "publisher, name, description, authors, license, homepage, repository";
+
+    /// <inheritdoc/>
+    public async ValueTask<IReadOnlyList<TazelPlugin>> ListAsync(CancellationToken cancellationToken)
+    {
+        await using NpgsqlConnection connection = await dataSource.OpenConnectionAsync(cancellationToken);
+        List<TazelPlugin> plugins = [];
+        await using (NpgsqlCommand command = new(
+            $"SELECT {PluginColumns} FROM viget_tazel_plugins ORDER BY publisher, name", connection))
+        await using (NpgsqlDataReader reader = await command.ExecuteReaderAsync(cancellationToken))
+        {
+            while (await reader.ReadAsync(cancellationToken))
+            {
+                plugins.Add(ReadPlugin(reader, []));
+            }
+        }
+
+        List<TazelPlugin> withVersions = [];
+        foreach (TazelPlugin plugin in plugins)
+        {
+            withVersions.Add(plugin with
+            {
+                Versions = await VersionsAsync(connection, null, plugin.Publisher, plugin.Name, cancellationToken)
+            });
+        }
+
+        return withVersions;
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask<TazelPlugin?> FindAsync(string publisher, string name, CancellationToken cancellationToken)
+    {
+        await using NpgsqlConnection connection = await dataSource.OpenConnectionAsync(cancellationToken);
+        TazelPlugin? plugin;
+        await using (NpgsqlCommand command = new(
+            $"SELECT {PluginColumns} FROM viget_tazel_plugins WHERE publisher = $1 AND name = $2", connection))
+        {
+            command.Parameters.AddWithValue(publisher);
+            command.Parameters.AddWithValue(name);
+            await using NpgsqlDataReader reader = await command.ExecuteReaderAsync(cancellationToken);
+            plugin = await reader.ReadAsync(cancellationToken) ? ReadPlugin(reader, []) : null;
+        }
+
+        return plugin is null
+            ? null
+            : plugin with { Versions = await VersionsAsync(connection, null, publisher, name, cancellationToken) };
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask<AddVersionResult> AddVersionAsync(
+        TazelPluginDescriptor descriptor,
+        string sha256,
+        long size,
+        DateTimeOffset publishedAt,
+        CancellationToken cancellationToken)
+    {
+        await using NpgsqlConnection connection = await dataSource.OpenConnectionAsync(cancellationToken);
+        await using NpgsqlTransaction transaction = await connection.BeginTransactionAsync(cancellationToken);
+        await using (NpgsqlCommand taken = new(
+            """
+            SELECT count(*) FROM viget_tazel_plugins
+            WHERE upper(publisher) = upper($1) AND upper(name) = upper($2) AND (publisher <> $1 OR name <> $2)
+            """,
+            connection,
+            transaction))
+        {
+            taken.Parameters.AddWithValue(descriptor.Publisher);
+            taken.Parameters.AddWithValue(descriptor.Name);
+            if ((long)(await taken.ExecuteScalarAsync(cancellationToken))! > 0)
+            {
+                return AddVersionResult.NameTaken;
+            }
+        }
+
+        await using (NpgsqlCommand plugin = new(
+            $"""
+            INSERT INTO viget_tazel_plugins ({PluginColumns}, updated_at)
+            VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+            ON CONFLICT (publisher, name) DO UPDATE SET
+                description = excluded.description,
+                authors = excluded.authors,
+                license = excluded.license,
+                homepage = excluded.homepage,
+                repository = excluded.repository,
+                updated_at = excluded.updated_at
+            """,
+            connection,
+            transaction))
+        {
+            plugin.Parameters.AddWithValue(descriptor.Publisher);
+            plugin.Parameters.AddWithValue(descriptor.Name);
+            plugin.Parameters.AddWithValue((object?)descriptor.Description ?? DBNull.Value);
+            plugin.Parameters.AddWithValue(descriptor.Authors.ToArray());
+            plugin.Parameters.AddWithValue((object?)descriptor.License ?? DBNull.Value);
+            plugin.Parameters.AddWithValue((object?)descriptor.Homepage ?? DBNull.Value);
+            plugin.Parameters.AddWithValue((object?)descriptor.Repository ?? DBNull.Value);
+            plugin.Parameters.AddWithValue(publishedAt);
+            await plugin.ExecuteNonQueryAsync(cancellationToken);
+        }
+
+        await using (NpgsqlCommand version = new(
+            """
+            INSERT INTO viget_tazel_plugin_versions (publisher, name, version, sha256, api_version, size, published_at)
+            VALUES ($1, $2, $3, $4, $5, $6, $7)
+            ON CONFLICT (publisher, name, version) DO NOTHING
+            """,
+            connection,
+            transaction))
+        {
+            version.Parameters.AddWithValue(descriptor.Publisher);
+            version.Parameters.AddWithValue(descriptor.Name);
+            version.Parameters.AddWithValue(descriptor.Version);
+            version.Parameters.AddWithValue(sha256);
+            version.Parameters.AddWithValue(descriptor.ApiVersion);
+            version.Parameters.AddWithValue(size);
+            version.Parameters.AddWithValue(publishedAt);
+            if (await version.ExecuteNonQueryAsync(cancellationToken) == 0)
+            {
+                // The plugin row is left as it was: the transaction is rolled back with the refusal.
+                return AddVersionResult.VersionExists;
+            }
+        }
+
+        await transaction.CommitAsync(cancellationToken);
+        return AddVersionResult.Added;
+    }
+
+    /// <inheritdoc/>
+    public async ValueTask<bool> SetYankedAsync(
+        string publisher,
+        string name,
+        string version,
+        bool yanked,
+        CancellationToken cancellationToken)
+    {
+        await using NpgsqlConnection connection = await dataSource.OpenConnectionAsync(cancellationToken);
+        await using NpgsqlCommand command = new(
+            """
+            UPDATE viget_tazel_plugin_versions SET yanked = $4
+            WHERE publisher = $1 AND name = $2 AND version = $3
+            """,
+            connection);
+        command.Parameters.AddWithValue(publisher);
+        command.Parameters.AddWithValue(name);
+        command.Parameters.AddWithValue(version);
+        command.Parameters.AddWithValue(yanked);
+        return await command.ExecuteNonQueryAsync(cancellationToken) == 1;
+    }
+
+    private static TazelPlugin ReadPlugin(NpgsqlDataReader reader, IReadOnlyList<TazelPluginVersion> versions) => new(
+        reader.GetString(0),
+        reader.GetString(1),
+        reader.IsDBNull(2) ? null : reader.GetString(2),
+        reader.GetFieldValue<string[]>(3),
+        reader.IsDBNull(4) ? null : reader.GetString(4),
+        reader.IsDBNull(5) ? null : reader.GetString(5),
+        reader.IsDBNull(6) ? null : reader.GetString(6),
+        versions);
+
+    private static async Task<IReadOnlyList<TazelPluginVersion>> VersionsAsync(
+        NpgsqlConnection connection,
+        NpgsqlTransaction? transaction,
+        string publisher,
+        string name,
+        CancellationToken cancellationToken)
+    {
+        await using NpgsqlCommand command = new(
+            """
+            SELECT version, sha256, api_version, size, published_at, yanked FROM viget_tazel_plugin_versions
+            WHERE publisher = $1 AND name = $2 ORDER BY published_at DESC, version DESC
+            """,
+            connection,
+            transaction);
+        command.Parameters.AddWithValue(publisher);
+        command.Parameters.AddWithValue(name);
+        await using NpgsqlDataReader reader = await command.ExecuteReaderAsync(cancellationToken);
+        List<TazelPluginVersion> versions = [];
+        while (await reader.ReadAsync(cancellationToken))
+        {
+            versions.Add(new TazelPluginVersion(
+                reader.GetString(0),
+                reader.GetString(1),
+                reader.GetInt32(2),
+                reader.GetInt64(3),
+                reader.GetFieldValue<DateTimeOffset>(4),
+                reader.GetBoolean(5)));
+        }
+
+        return versions;
+    }
+}
diff --git a/apps/api/ViGet/TazelPluginCatalog.cs b/apps/api/ViGet/TazelPluginCatalog.cs
new file mode 100644
index 0000000..e6fa2e9
--- /dev/null
+++ b/apps/api/ViGet/TazelPluginCatalog.cs
@@ -0,0 +1,177 @@
+// SPDX-FileCopyrightText: 2026 Progmasoft <support@progmasoft.com>
+// SPDX-License-Identifier: AGPL-3.0-or-later WITH AdditionRef-Progmasoft-Patent-Grant-1.1
+
+namespace Progmasoft.Progmaweb.Api.ViGet;
+
+/// <summary>One published version of a Tazel plugin.</summary>
+/// <param name="Version">The version.</param>
+/// <param name="Sha256">The SHA-256 digest of its JAR, in lower-case hex.</param>
+/// <param name="ApiVersion">The plugin API of Tazel it was built for.</param>
+/// <param name="Size">The size of its JAR in bytes.</param>
+/// <param name="PublishedAt">When it was published.</param>
+/// <param name="Yanked">Whether it was yanked: Tazel takes it only when a project names it.</param>
+internal sealed record TazelPluginVersion(
+    string Version,
+    string Sha256,
+    int ApiVersion,
+    long Size,
+    DateTimeOffset PublishedAt,
+    bool Yanked);
+
+/// <summary>A Tazel plugin of the catalog, described by the descriptor of its newest publication.</summary>
+/// <param name="Publisher">The Progmasoft Account it is published under.</param>
+/// <param name="Name">Its name.</param>
+/// <param name="Description">What it does.</param>
+/// <param name="Authors">Its authors.</param>
+/// <param name="License">An SPDX license expression.</param>
+/// <param name="Homepage">An https address of the plugin.</param>
+/// <param name="Repository">An https address of its sources.</param>
+/// <param name="Versions">Its versions, newest publication first.</param>
+internal sealed record TazelPlugin(
+    string Publisher,
+    string Name,
+    string? Description,
+    IReadOnlyList<string> Authors,
+    string? License,
+    string? Homepage,
+    string? Repository,
+    IReadOnlyList<TazelPluginVersion> Versions)
+{
+    /// <summary>The newest version that is not yanked, or the newest of all when every one is.</summary>
+    public TazelPluginVersion Latest =>
+        Versions.Where(version => !version.Yanked).DefaultIfEmpty(Versions[0]).First();
+}
+
+/// <summary>What adding a version to the catalog did.</summary>
+internal enum AddVersionResult
+{
+    /// <summary>The version was added.</summary>
+    Added,
+
+    /// <summary>The plugin has this version already; a version is never replaced.</summary>
+    VersionExists,
+
+    /// <summary>A plugin of the publisher has the same name in other letter case.</summary>
+    NameTaken,
+}
+
+/// <summary>The Tazel plugins of ViGet: their descriptions and versions. The JARs live in files beside it.</summary>
+internal interface ITazelPluginCatalog
+{
+    /// <summary>Every plugin, ordered by publisher and name.</summary>
+    ValueTask<IReadOnlyList<TazelPlugin>> ListAsync(CancellationToken cancellationToken);
+
+    /// <summary>A plugin by its exact publisher and name.</summary>
+    ValueTask<TazelPlugin?> FindAsync(string publisher, string name, CancellationToken cancellationToken);
+
+    /// <summary>Adds a version, and describes the plugin with the descriptor of that version.</summary>
+    ValueTask<AddVersionResult> AddVersionAsync(
+        TazelPluginDescriptor descriptor,
+        string sha256,
+        long size,
+        DateTimeOffset publishedAt,
+        CancellationToken cancellationToken);
+
+    /// <summary>Yanks a version, or takes the yank back.</summary>
+    /// <returns>Whether the plugin has the version.</returns>
+    ValueTask<bool> SetYankedAsync(
+        string publisher,
+        string name,
+        string version,
+        bool yanked,
+        CancellationToken cancellationToken);
+}
+
+/// <summary>A catalog that lives as long as the process, for development and tests.</summary>
+internal sealed class InMemoryTazelPluginCatalog : ITazelPluginCatalog
+{
+    private readonly Lock gate = new();
+    private readonly Dictionary<(string Publisher, string Name), TazelPlugin> plugins = [];
+
+    /// <inheritdoc/>
+    public ValueTask<IReadOnlyList<TazelPlugin>> ListAsync(CancellationToken cancellationToken)
+    {
+        lock (gate)
+        {
+            return ValueTask.FromResult<IReadOnlyList<TazelPlugin>>(plugins.Values
+                .OrderBy(plugin => plugin.Publisher, StringComparer.Ordinal)
+                .ThenBy(plugin => plugin.Name, StringComparer.Ordinal)
+                .ToList());
+        }
+    }
+
+    /// <inheritdoc/>
+    public ValueTask<TazelPlugin?> FindAsync(string publisher, string name, CancellationToken cancellationToken)
+    {
+        lock (gate)
+        {
+            return ValueTask.FromResult(plugins.GetValueOrDefault((publisher, name)));
+        }
+    }
+
+    /// <inheritdoc/>
+    public ValueTask<AddVersionResult> AddVersionAsync(
+        TazelPluginDescriptor descriptor,
+        string sha256,
+        long size,
+        DateTimeOffset publishedAt,
+        CancellationToken cancellationToken)
+    {
+        lock (gate)
+        {
+            (string, string) key = (descriptor.Publisher, descriptor.Name);
+            if (!plugins.ContainsKey(key) && plugins.Keys.Any(existing =>
+                    string.Equals(existing.Publisher, descriptor.Publisher, StringComparison.OrdinalIgnoreCase) &&
+                    string.Equals(existing.Name, descriptor.Name, StringComparison.OrdinalIgnoreCase)))
+            {
+                return ValueTask.FromResult(AddVersionResult.NameTaken);
+            }
+
+            List<TazelPluginVersion> versions = plugins.TryGetValue(key, out TazelPlugin? existingPlugin)
+                ? [.. existingPlugin.Versions]
+                : [];
+            if (versions.Any(version => version.Version == descriptor.Version))
+            {
+                return ValueTask.FromResult(AddVersionResult.VersionExists);
+            }
+
+            versions.Insert(
+                0, new TazelPluginVersion(descriptor.Version, sha256, descriptor.ApiVersion, size, publishedAt, false));
+            plugins[key] = new TazelPlugin(
+                descriptor.Publisher,
+                descriptor.Name,
+                descriptor.Description,
+                descriptor.Authors,
+                descriptor.License,
+                descriptor.Homepage,
+                descriptor.Repository,
+                versions);
+            return ValueTask.FromResult(AddVersionResult.Added);
+        }
+    }
+
+    /// <inheritdoc/>
+    public ValueTask<bool> SetYankedAsync(
+        string publisher,
+        string name,
+        string version,
+        bool yanked,
+        CancellationToken cancellationToken)
+    {
+        lock (gate)
+        {
+            if (!plugins.TryGetValue((publisher, name), out TazelPlugin? plugin) ||
+                plugin.Versions.All(existing => existing.Version != version))
+            {
+                return ValueTask.FromResult(false);
+            }
+
+            plugins[(publisher, name)] = plugin with
+            {
+                Versions = [.. plugin.Versions.Select(existing =>
+                    existing.Version == version ? existing with { Yanked = yanked } : existing)]
+            };
+            return ValueTask.FromResult(true);
+        }
+    }
+}
diff --git a/apps/api/ViGet/TazelPluginDescriptor.cs b/apps/api/ViGet/TazelPluginDescriptor.cs
new file mode 100644
index 0000000..eddd541
--- /dev/null
+++ b/apps/api/ViGet/TazelPluginDescriptor.cs
@@ -0,0 +1,134 @@
+// SPDX-FileCopyrightText: 2026 Progmasoft <support@progmasoft.com>
+// SPDX-License-Identifier: AGPL-3.0-or-later WITH AdditionRef-Progmasoft-Patent-Grant-1.1
+
+using System.IO.Compression;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace Progmasoft.Progmaweb.Api.ViGet;
+
+/// <summary>
+/// The descriptor of a Tazel plugin, <c>META-INF/tazel-plugin.properties</c> of its JAR, as Tazel reads it, with the
+/// fields ViGet shows on the page of the plugin.
+/// </summary>
+/// <param name="Publisher">The Progmasoft Account the plugin is published under.</param>
+/// <param name="Name">The name of the plugin; one identifier.</param>
+/// <param name="Version">An exact semantic version.</param>
+/// <param name="ApiVersion">The plugin API of Tazel it was built for.</param>
+/// <param name="Description">What the plugin does.</param>
+/// <param name="Authors">The authors, in the order of the descriptor.</param>
+/// <param name="License">An SPDX license expression.</param>
+/// <param name="Homepage">An https address of the plugin.</param>
+/// <param name="Repository">An https address of its sources.</param>
+internal sealed partial record TazelPluginDescriptor(
+    string Publisher,
+    string Name,
+    string Version,
+    int ApiVersion,
+    string? Description,
+    IReadOnlyList<string> Authors,
+    string? License,
+    string? Homepage,
+    string? Repository)
+{
+    /// <summary>Where the descriptor lies in the JAR.</summary>
+    public const string DescriptorEntry = "META-INF/tazel-plugin.properties";
+
+    /// <summary>The service entry that names the class Tazel loads.</summary>
+    public const string ServiceEntry = "META-INF/services/com.progmasoft.api.tazel.dsl.plugin.ProjectPlugin";
+
+    /// <summary>Whether a text is one identifier, as Tazel requires of a publisher and a plugin name.</summary>
+    public static bool IsIdentifier(string value) => IdentifierPattern().IsMatch(value);
+
+    /// <summary>Whether a text is an exact semantic version, as Tazel requires of a plugin version.</summary>
+    public static bool IsVersion(string value) => VersionPattern().IsMatch(value);
+
+    /// <summary>Reads and checks the descriptor of a plugin JAR.</summary>
+    /// <param name="jar">The bytes of the JAR.</param>
+    /// <param name="descriptor">The descriptor, when the JAR is a valid plugin.</param>
+    /// <returns>Why the JAR is refused, or <see langword="null"/> when it is valid.</returns>
+    public static string? TryRead(byte[] jar, out TazelPluginDescriptor? descriptor)
+    {
+        descriptor = null;
+        IReadOnlyDictionary<string, string> properties;
+        try
+        {
+            using ZipArchive archive = new(new MemoryStream(jar, writable: false), ZipArchiveMode.Read);
+            ZipArchiveEntry? entry = archive.GetEntry(DescriptorEntry);
+            if (entry is null)
+            {
+                return $"The JAR has no {DescriptorEntry}.";
+            }
+
+            ZipArchiveEntry? service = archive.GetEntry(ServiceEntry);
+            if (service is null || service.Length == 0)
+            {
+                return $"The JAR has no {ServiceEntry}.";
+            }
+
+            using StreamReader reader = new(entry.Open(), Encoding.Latin1);
+            properties = JavaProperties.Parse(reader.ReadToEnd());
+        }
+        catch (InvalidDataException)
+        {
+            return "The file is not a JAR.";
+        }
+        catch (FormatException error)
+        {
+            return $"The descriptor is not a properties file: {error.Message}";
+        }
+
+        string? Text(string key) =>
+            properties.TryGetValue(key, out string? value) && !string.IsNullOrWhiteSpace(value) ? value.Trim() : null;
+
+        string? publisher = Text("publisher");
+        string? name = Text("name");
+        string? version = Text("version");
+        if (publisher is null || !IsIdentifier(publisher))
+        {
+            return "The descriptor needs a publisher that is one identifier.";
+        }
+
+        if (name is null || !IsIdentifier(name))
+        {
+            return "The descriptor needs a name that is one identifier.";
+        }
+
+        if (version is null || !IsVersion(version))
+        {
+            return "The descriptor needs an exact semantic version.";
+        }
+
+        if (!int.TryParse(Text("apiVersion"), out int apiVersion) || apiVersion < 1)
+        {
+            return "The descriptor needs an API version.";
+        }
+
+        List<string> authors = [];
+        for (int index = 0; Text($"author.{index}") is { } author; index++)
+        {
+            authors.Add(author);
+        }
+
+        string? homepage = Text("homepage");
+        string? repository = Text("repository");
+        foreach ((string key, string? address) in new[] { ("homepage", homepage), ("repository", repository) })
+        {
+            if (address is not null &&
+                (!Uri.TryCreate(address, UriKind.Absolute, out Uri? uri) || uri.Scheme != Uri.UriSchemeHttps))
+            {
+                return $"The {key} of the descriptor is not an https address.";
+            }
+        }
+
+        descriptor = new TazelPluginDescriptor(
+            publisher, name, version, apiVersion, Text("description"), authors, Text("license"), homepage, repository);
+        return null;
+    }
+
+    [GeneratedRegex("^[A-Za-z_][A-Za-z0-9_]*$")]
+    private static partial Regex IdentifierPattern();
+
+    [GeneratedRegex(@"^(?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*)(?:-[0-9A-Za-z.-]+)?$")]
+    private static partial Regex Ve