docs: add rent costs table to README

[dev-jodee]

Summary

• Add a ## Rent Costs section to the README documenting approximate per-flow account-creation rent (in SOL), so integrators can estimate setup costs.
• Covers: enable authority, create plan, subscribe, grant fixed delegation, grant recurring delegation.
• Notes that rent is recoverable when the delegation / plan / authority is closed.

Docs-only change.

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Project	Deployment	Actions	Updated (UTC)
solana-subscriptions-program	Ready	Preview, Comment	Jun 4, 2026 2:13pm

[github-actions]

Compute Unit Report

Instruction	Samples	Min CUs	Max CUs	Avg CUs	Est Cost (Low) [SOL]	Est Cost (Med) [SOL]	Est Cost (High) [SOL]
cancel_subscription	22	1720	2030	1919	0.000005000	0.000005076	0.000005959
close_subscription_authority	10	1803	1833	1806	0.000005000	0.000005072	0.000005903
create_fixed_delegation	41	3517	14022	5411	0.000005001	0.000005216	0.000007705
create_plan	97	3436	13949	5016	0.000005001	0.000005200	0.000007508
create_recurring_delegation	29	3553	9555	4694	0.000005001	0.000005187	0.000007347
delete_plan	9	359	359	359	0.000005000	0.000005014	0.000005179
init_subscription_authority	173	6226	20496	9274	0.000005002	0.000005370	0.000009637
resume_subscription	3	1723	1723	1723	0.000005000	0.000005068	0.000005861
revoke_delegation	19	255	519	353	0.000005000	0.000005014	0.000005176
subscribe	32	6485	12485	7429	0.000005002	0.000005297	0.000008714
transfer_fixed	9	5476	12840	8197	0.000005002	0.000005327	0.000009098
transfer_recurring	19	5591	11452	6829	0.000005002	0.000005273	0.000008414
transfer_subscription	10	5799	10338	7193	0.000005002	0.000005287	0.000008596
update_plan	22	424	503	477	0.000005000	0.000005019	0.000005238

Generated: 2026-06-04

[greptile-apps]

Greptile Summary

This PR adds a ## Rent Costs section to the README documenting approximate per-flow account-creation rent (in SOL) for five flows. All five rent values have been verified against the current account struct sizes in the Rust source and are mathematically correct.

• Adds a five-row Markdown table mapping each flow to the single account it creates and its rent-exempt minimum; account names and SOL figures are accurate.
• Appends a callout note clarifying that "Subscribe and delegation flows" (rows 3–5) require a pre-existing SubscriptionAuthority, and quantifies the extra 0.00162864 SOL cost for first-time users.
• The "Merchant creates a plan" row correctly omits the SA prerequisite, since Plan PDAs are keyed independently of any SubscriptionAuthority.

Confidence Score: 5/5

Documentation-only change; all rent figures and account names have been independently verified against the current Rust struct sizes.

The change adds only a Markdown table and a prose note to the README. Every SOL value in the table was cross-checked against the compile-time-asserted account lengths in the Rust state files and the standard Solana rent formula — all five figures are exact. The account names match the actual struct names in the codebase, and the prerequisite note is correctly scoped to the three flows that require a SubscriptionAuthority.

No files require special attention.

Important Files Changed

Filename	Overview
README.md	Adds a Rent Costs table with five flows; all account names and SOL figures verified correct against Rust struct sizes; SA prerequisite note is accurate and scoped correctly to subscription/delegation flows only.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    SA["Enable authority\nSubscriptionAuthority\n0.00162864 SOL"]
    Plan["Merchant creates a plan\nPlan\n0.00430824 SOL"]
    Sub["Subscribe to a plan\nSubscriptionDelegation\n0.00196968 SOL"]
    Fixed["Grant fixed delegation\nFixedDelegation\n0.00219240 SOL"]
    Recurring["Grant recurring delegation\nRecurringDelegation\n0.00235944 SOL"]

    SA -->|prerequisite| Sub
    SA -->|prerequisite| Fixed
    SA -->|prerequisite| Recurring
    Plan -->|prerequisite| Sub

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