Split the HTTPS transport into an optional pg_git_https extension

[seanwevans]

Stacked on #70 — it needs that PR's canonical upgrade-script naming and DATA wiring, without which the 0.4.0 → 0.5.0 script could not be found or installed. Review/merge #70 first; the base is set accordingly.

The problem

pg_git.control listed plpython3u in requires, so CREATE EXTENSION pg_git failed on every managed PostgreSQL. plpython3u is untrusted, needs superuser, and is not offered by RDS, Cloud SQL, Supabase or Neon.

The only thing that needed it was the HTTPS transport in sql/functions/014-https.sql — three objects out of 141.

The fix

CREATE EXTENSION pg_git;        -- core VCS, trusted deps only
CREATE EXTENSION pg_git_https;  -- optional, needs plpython3u

Core pg_git now requires plpgsql, pgcrypto and pg_trgm, all of which managed providers offer.

Why the version bump

Core goes to 0.5.0 because its object set changes; leaving it at 0.4.0 would mean two databases reporting the same version with different contents. pg_git_https starts at 0.1.0.

Preserving stored credentials

sql/pg_git--0.4.0--0.5.0.sql releases pggit.credentials, pggit.store_credentials and pggit.http_fetch from pg_git without dropping them, so encrypted credentials survive; pg_git_https adopts them on install.

Two details worth a reviewer's eye:

• The companion script adopts before it creates. While an extension script is running, PostgreSQL rejects both CREATE ... IF NOT EXISTS and CREATE OR REPLACE against an object the extension does not already own ("is not a member of extension"). ALTER EXTENSION ... ADD has to come first or the upgrade path does not work at all.
• The ALTER EXTENSION ... DROP statements are guarded. A database that reaches 0.4.0 through this tree's upgrade chain never had the HTTPS objects; one installed from the released 0.4.0 script did. Both end at the same 0.5.0.

Verification

On PostgreSQL 16, on a cluster with no plpython3u available at all:

Scenario	Result
CREATE EXTENSION pg_git CASCADE	succeeds, 138 objects, no HTTPS objects present
0.4.0 install with a stored credential → bare ALTER EXTENSION pg_git UPDATE → CREATE EXTENSION pg_git_https	all three objects re-owned by pg_git_https, credential still decryptable
fresh CREATE EXTENSION pg_git_https	creates the same three objects
DROP EXTENSION pg_git_https	core's 138 objects intact
replay 0.1.0 → 0.5.0 vs. fresh 0.5.0	identical object sets

Also updated

meta.json (second provides entry, plpython3u moved to recommends), README.md, sql/README.md, CONTRIBUTING.md, Dockerfile comment, and the two tests that referenced the dependency — https_fetch_test.sql now installs the companion itself, so it stays the only test that needs plpython3u.

🤖 Generated with Claude Code

https://claude.ai/code/session_017nq3xZcPqSTKtskyP2DzkK

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