Declare only the tables and columns pixa writes and reads (closes #310)

Removes output_content and request_cache, which nothing writes, and every
column that was written but never read: the host, path, query, content_type
and fetched_at of source_content, the content_type and created_at of
variant_content, and the status_code, error_message and fetched_at of
negative_cache.

StoreSource no longer takes the fetch result and LookupSource returns only
the source key. StoreVariant no longer takes a content type and
StoreNegative no longer takes a status code or message, so
extractStatusCode and the status constants, which only fed status_code,
are gone. Reconciliation adopts a variant file without opening it, as its
row no longer records a content type. Tests that set or checked a removed
column follow.

Model: opus-5-5

internal/db/migrations/001_schema.sql

@@ -6,12 +6,7 @@
 -- is the SHA-256 of the source's host, path and query
 CREATE TABLE IF NOT EXISTS source_content (
     source_key TEXT PRIMARY KEY,
-    source_host TEXT NOT NULL,
-    source_path TEXT NOT NULL,
-    source_query TEXT NOT NULL DEFAULT '',
-    content_type TEXT NOT NULL,
     size_bytes INTEGER NOT NULL,
-    fetched_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     last_accessed_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
 CREATE INDEX IF NOT EXISTS idx_source_content_last_accessed
@@ -27,8 +22,6 @@ CREATE INDEX IF NOT EXISTS idx_source_content_last_accessed
 CREATE TABLE IF NOT EXISTS variant_content (
     cache_key TEXT PRIMARY KEY,
     size_bytes INTEGER NOT NULL,
-    content_type TEXT NOT NULL,
-    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
     last_accessed_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
 CREATE INDEX IF NOT EXISTS idx_variant_content_last_accessed
@@ -102,46 +95,14 @@ BEGIN
     WHERE id = 1;
 END;
 
--- Output/transformed content blobs
--- Not written: transformed images are stored in cache/variants and
--- tracked in variant_content above.
-CREATE TABLE IF NOT EXISTS output_content (
-    content_hash TEXT PRIMARY KEY,
-    content_type TEXT NOT NULL,
-    size_bytes INTEGER NOT NULL,
-    fetched_at DATETIME DEFAULT CURRENT_TIMESTAMP
-);
-
--- Request cache - maps full request params to output content
-CREATE TABLE IF NOT EXISTS request_cache (
-    id INTEGER PRIMARY KEY AUTOINCREMENT,
-    cache_key TEXT NOT NULL UNIQUE,
-    source_metadata_id INTEGER NOT NULL,
-    output_hash TEXT NOT NULL,
-    width INTEGER NOT NULL,
-    height INTEGER NOT NULL,
-    format TEXT NOT NULL,
-    quality INTEGER NOT NULL DEFAULT 85,
-    fit_mode TEXT NOT NULL DEFAULT 'cover',
-    fetched_at DATETIME DEFAULT CURRENT_TIMESTAMP,
-    access_count INTEGER NOT NULL DEFAULT 1,
-    FOREIGN KEY (source_metadata_id) REFERENCES source_metadata(id),
-    FOREIGN KEY (output_hash) REFERENCES output_content(content_hash)
-);
-CREATE INDEX IF NOT EXISTS idx_request_cache_key ON request_cache(cache_key);
-CREATE INDEX IF NOT EXISTS idx_request_cache_source ON request_cache(source_metadata_id);
-CREATE INDEX IF NOT EXISTS idx_request_cache_output ON request_cache(output_hash);
-CREATE INDEX IF NOT EXISTS idx_request_cache_fetched ON request_cache(fetched_at);
-
--- Negative cache for failed fetches (404s, timeouts, etc.)
+-- Negative cache: source URLs whose fetch failed with an upstream error
+-- status, or whose first bytes did not match their Content-Type. pixa does
+-- not fetch such a URL again until its row expires.
 CREATE TABLE IF NOT EXISTS negative_cache (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
     source_host TEXT NOT NULL,
     source_path TEXT NOT NULL,
     source_query TEXT NOT NULL DEFAULT '',
-    status_code INTEGER NOT NULL,
-    error_message TEXT,
-    fetched_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     expires_at DATETIME NOT NULL,
     UNIQUE(source_host, source_path, source_query)
 );