fix: increase secret value column from VARCHAR(255) to TEXT

[DragonBot00]

Fix: Increase secret.value column from VARCHAR(255) to TEXT

Problem

Fixes #5353

When SECRET_MANAGER_TYPE=db, the secret.value column in the Secret SQLModel was defined as value: str, which SQLModel maps to VARCHAR(255) by default. This causes any secret value exceeding 255 characters (such as OAuth access tokens, refresh tokens, or JWT tokens) to be silently truncated at the database level.

Root Cause

In keep/api/models/db/secret.py, the value field lacked an explicit SQLAlchemy column type:

# Before (defaults to VARCHAR(255))
value: str

Solution

Explicitly set the column type to sa.Text (unlimited length):

# After (TEXT - no length limit)
value: str = Field(sa_column=sa.Column(sa.Text, nullable=False))

Changes

1. keep/api/models/db/secret.py — Changed value field to use sa.Text instead of the implicit VARCHAR(255).
2. keep/api/models/db/migrations/versions/2026-04-01-07-55_a1b2c3d4e5f6.py — Added Alembic migration to ALTER TABLE secret ALTER COLUMN value TYPE TEXT on existing deployments.

Testing

• New deployments: The Secret table will be created with a TEXT column for value.
• Existing deployments: Running alembic upgrade head will apply the migration and widen the column with no data loss.

Impact

• No breaking changes — TEXT columns are fully backward-compatible with VARCHAR.
• Fixes silent truncation of OAuth tokens and any other secrets > 255 chars.

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[DragonBot00]

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